Searching for info regarding Daniel Donovan of Ballymartin, born 1828

Hello,

I am searching for any information about my 3x great grandfather, Daniel Donovan of Ballymartin.  He was born in 1828, according to his US Naturalization papers.  He was married to Ellen Crowly or Crowley, born in 1835.  I have seen it spelled both ways in my family's records.  

I do not know if Daniel and Ellen married in  Ireland, as I have been unsuccessful in finding any records for this marriage on the Irish genealogy website or on Ancestry, Rootsweb, and Find My Past.  I have been unsuccessful in finding any records for a marriage in the US and in Canada as well. 

I know that the records for Daniel's home parish only go back to 1833, so I am hoping that someone may know something about my ancestors.  

Facts I CAN provide include the following:  

Daniel Donovan was born in 1828 in Ballymartin, Cork, Ireland.  He became a US citizen 17 September 1857 in Rutledge, Rutledge County Vermont and worked as a quarryman there.  Sometime before 1859, he married Ellen Crowley They had seven children in 11 years.  These include: 

1. Cornelius, 1859
2. Terrance, 1860
3. Timothy, 1860
4. Patrick John, 1862 (my great-great-grandfather, a railway engineer in Illinois and Iowa)
5. Ellen, 1866
6. Mary Ann, 1867
7. Kate, 1870

Daniel died on April 26, 1880, in West Rutland, Vermont; age at death: 53 His headstone reads "A native of the parish of Ballymartin, County Cork, Ireland.  He is buried in St. Brigid's Cemetery, Rutland County, Vermont, USA.  

Any help would be greatly appreciated! 

E. Howell