Carroll/O'Carroll's County Louth

Looking to find where my great-grandfather William Joseph Carroll born on 6 Jun 1848 or 1850 was born.  My Great Aunt, his grand-daughter, told me in 1979 via a letter that her grandfather was from County Louth.  I was young then and I question now what did that mean?  Was he born in County Louth?  Was he from Louth, County Louth? Or did he possibly immigrate from County Louth and was from somewhere else?  His son, William Joseph Carroll (same name), told me that his father, the above William was born in Ireland, making my Grandfather 1st generation American born. I always thought that meant that both William's were in America and no one else before them.  Through census records I have uncovered that the father and the grandfather of Wm. J. Carroll b. 1848 or 1850 have also come to America as well as several siblings of the 1848 born Wm.  I only now assume that they came from Louth like William, but they could have come from somewhere else in Ireland.  The elder Wm.'s father was Nicholas (James?) Carroll born about 1815.  He was married to Catherine (Kate) McKenna b. abt. 1822 in Ireland, d. 3 Feb 1900 in Phila., PA, USA.  Since Wm. was born in Ireland, they had to marry in Ireland as well.  I have the following children for Nicholas and Catherine:  Michael J. Carroll b. abt. 1846- d.1893 b. Ireland, d. PA, USA; Patrick Henry Carroll b. May 1846 -1918 (twin of Michael or close in age?) b. Ireland, d. Atlantic City, NJ, USA; William Joseph Carroll (my great) b.6 Jun 1848 or 1850 Louth?, Ireland, d. Philadelphia, PA, USA; Rosana or Rose Anna Carroll b. PA, USA 1853, d. possibly in Beverly, Burlington, NJ, USA after 1950; John Carroll b. & d. Phila., PA, USA b. 29 Jan 1854, d. 18 Aug 1862; Nicholas James Carroll b. & d. Phila., PA, USA, b. 26 Oct 1855, d. 5 Jan 1896; James Nicholas Carroll b. & d. Phila., PA, USA, b. 25 Feb 1858, d. 8 Dec 1925; Thomas Henry Carroll b. & d. Phila., PA, USA, b. 29 May 1860, d. 17 Jan 1939; Mary Jane Carroll b. 1 Sep 1863 Phila., PA, USA, d. unknown.  She was still living in the 1930 US census for Phila.  She was widowed by then, her husband being Thomas Augustus Murphy 1864-1926.  I do  not know if there were any more children born in Ireland or even born in the US that mayhave died young.  The family name was O'Carroll, but at what time, I do not know.  Nicholas J. Carroll's father, John Carroll came to the USA.  I have his death info.  Died 21 Oct 1858 Phila., PA, USA.  His only other child that I know of besides Nicholas is John Carroll b. Sep 1835 in Ireland and D. 31 Mar 1910 in New York, NY, USA.  County Armagh is a possible birth location for the Patriarch, John.  The family was Roman Catholic and many of the men were blacksmiths, horseshoers or jewelers.  I do have spouse information on the above, but feel this is getting too long already so I'll wait until someone asks specific questions to furnish that information.  I also have photos of Wm. J., Patrick Henry and Thomas Henry.  The majority of the family settled in Philadelphia, PA, USA.  My dad, another Wm. J. Carroll was born & died in Phila.  I also was born in Phila.  Any information would be so welcomed.  When I search Louth there are just too many Carroll's with the same first names.  It is so overwhelming and I'm not sure if I have the correct people.  I do have as many documents that I can find on the US side, (been looking since 1979) but nothing specifies the exact location in ireland, not even marriage documents.  Thank You so much for having a site like this, Pat (Patricia) Carroll Bennett