I am researching Bresnahan's from County Cork also. This is my line:
John Bresnahan b. 18 May 1836 County Cork, Ireland d. 18 Mar 1912 in Ft. Wayne, Indiana. John married Mary Toomey who was b. 15 Aug 1837 in Fermoy, County Cork and d. 19 Jun 1927 in Ft. Wayne also.
John's father was Maurice and mother was Bridget Connell. I have no information as to whether they left Ireland or not. I know nothing about them at all.
John and Mary's children are:
John b. 18 Jan 1866 who married Florence
Mary b. 29 Dec 1869
Thomas b. 19 Aug 1871 m. Mary Callahan
Patrick (my g grandfather) b. 11 Mar 1873 m. Julie Flynn
Johanna b. 3 Aug 1862 m. Jule (or Julian) Stier
Edward b. 1881
Have you come across any of these names in your Bresnahan/Cork research?