Nancy,
My great grandfather was Thomas Michael McCarthy, baptized 1 Dec 1865 in Ballyvourney, County Cork. He immigrated to Wilmington, Delaware, around 1887. On his Wilmington, DE, marriage record in 1894 his birthplace is listed as "Ballywoden," County Cork, but I have never been able to locate a place by that name. He married a Margaret Tuomey/Toomey/Twomey, also listed as from Ballywoden, but I have located a record for her on RootsIreland.ie indicating she was baptized on 19 Jan 1870 at Kilnamartyra, County Cork.
This couple was closely allied with the families you mention--probably related.
Baptismal sponsors for Thomas were Jeremiah Lynch and Hanora (last name not recorded) in 1865 in Ballyvourney.
Baptismal sponsors for Thomas' sister Julia McCarthy were Daniel Lynch and Margaret Sullivan in 1873 in Ballyvourney. (She was born in Derrylahan, Ballyvourney.) Baptismal sponsors for Thomas' brother Cornelius McCarthy were Timothy McCarthy and Margaret Lynch in 1876 in Ballyvourney.
At the time of the 1900 US census Thomas McCarthy's household in Wilmington, DE, included his wife Maggie and children (Dennis, Timothy, Johannah, Edward, and Thomas), along with boarders, Timothy O'Herley (b. May 1871, Ireland) and Patrick O'Herley (b. Dec 1876, Ireland), and servant, Ella Cronan (b. Jun 1872, Ireland).
According to the naturalization papers of Patrick Herlihy, he immigrated to the US on 15 Apr 1900 and naturalized on 8 Oct 1906. This document states that he was born on 17 Apr 1877 in Ballyvourney, Cork, and his wife Catherine was from County Mayo. On RootsIreland.ie there is a baptismal record for Patrick Herlihy, son of Thomas Herlihy and Mary McCarthy, baptized 13 Apr 1877 in Ballyvourney. I have also found a baptismal record for Timothy Herlihy, son of Thomas Herlihy and Mary McCarthy, baptized on 18 Jan 1872 at "Moonabeg," Ballyvourney, Cork.
Timothy Herlihy went on to marry fellow 1900 housemate Ella Cronan/Cronin in about 1901.
Other closely allied families I have found include: Quill and [O']Connell.
Please email me if you would like to discuss further.
Anita
abackus98 at yahoo.com