Looking for my ancestors that came to USA in 1860's

Do you have US death certs for any of the family, or marriage certs for any of the children ?

These could could provide some very useful cues to help your search - e.g. Ellen's maiden name, and in the case of certs for Ellen and Edward names of their parents.

Problem is that if 'Cork' is where your ancestors came from can mean the city or county, and it's the largest county in Ireland, and without know a more specific location, i.e. town or parish, there are over 100 parishes to search.. and many Hennessy families.

p.s. do you have years of birth, even estimated, for the children you mentioned ?

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

This is what I have for Edward Hennessy:  Born in Irish Free State about 1830, Died in Oil City, Pennsylvania, USA on 17 May 1890.  He and Ellen had 5 children, the first four were all born in Irish Free State -

Edward E Hennessy (my great-grandfather born 13 Feb 1856 in Irish Free State, and died 8 Jul 1937 in Sacramento, CA, USA. I do have a California Death Index Record for my great grandfather, and a copy 

Eliza Hennessy born 1859 in Ireland (cannot find anything about her except when she arrived in New York USA with Ellen and oldest 3 siblings on 29 Aug 1866 on ship "Pennsylvania" which departed from Liverpool, England and Queenstown, Ireland)

Michael Hennessy born about 1860 in Ireland (no other info except arrival in New York;

Dennis Hennessy born about 1861 in Ireland and was listed on US census of 1870 as living in Oil City, Pennsylvania.

The last child of Edward & Ellen was born in Pennsylvania about 1868 - no other information that I can find.

I do not have birth certificates for any of Edward & Ellen's children, nor death certificates.

Does the death cert for Edward jnr. include his parents names - particularly mother's surname ?

There's a public tree on Ancestry which matches most of the details you've mentioned for Edward E. including dates and his parents names, siblings etc and gives mother's maiden name as O'Brien. The tree doesn't show any details on a location in Ireland or any Irish sources that I can see, but will check in a bit more detail later on..

I've had a closer look at that public tree on Ancestry - and found a copy cert of a marriage attached for an Edward Hennesy and an Eleanor(Ellen) Brien, on the 28th May 1854. Also handwritten on the back of the document, and appears to be the Parish Secretary's handwriting,  is a note of a baptism for an Edward Hennessey to Edward and Eleanor/Ellen on the 10th February 1856, and so very close to the date you mentioned. Dates are often inaccurate in later records, but maybe in this case they were just switched - i.e. 10th might be date of birth, and 13th date of baptism ?

The parish noted on the form is Bagnalstown, which is in Co. Carlow. Also noted on the cert in the same handwriting is 'Bohermore', which I suspect is a reference to the townland of that name (Dunleckny civil parish) where some of the family lived.

Some Church of Ireland records for Co. Carlow are available online on the irishGenealogy website, but no RC records available for the county through that website or RootsIreland pay-website (except some border parishes) at the moment. LDS/Family History Centres appear to have a film of the registers for this parish, so might be worth checking into those if there's a FHC near you 

The user name is chouston20, and I'd say definitely worth trying to make contact with them, maybe through a message on Ancestry or see they can be located with online searching..