Corbett and Gahagan families 1800-1850

I have been researching the Corbett and Gahagan lines for about a year now and have hit a dead end.

I am looking for information on their birth places and their parents and siblings. I still use familysearh.org, irish family history foundation, ancestry.com, and occasionally, Irish Times.

I am looking for information on Patrick Corbett, born 1822 in County Waterford. Information from Irish Times states he most likely came from northern Waterford, near the border with southern Tipperary, possibly near Lismore. I have not found a baptismal record or Parish record for him.

He shows up in a Federal Census in 1855, in Randolph, New York, USA. However, family notes say he may have emigrated between 1845 and1850. He was a farmer in Randolph. I have found no emigration record for him either. Sites pertaining to pre-Ellis Island records have no information on him.  In his first born's obituary, a daughter, Mary, it is stated that He, his wife, Nora Gahagan and daughter Mary moved to Randolph from Little Valley, New York about 1851 or 1852. His birthdate ranges from 1820 to 1825 in the Federal Census' from 1855 to 1880 (He died in 1888) Family notes give his birthdate as 1822.

His wife, Nora Gahagan was to have been born in 1820 in the Lismore area of Waterford. She was to have emigrated at the age of 25 in 1845 or 1846. She too, has different ages and different first names in most of the Federal Census'. Her first name varies with Hanora, Honora, Hannah, Honor and Nora. Her obituary in 1902 lists her first name as Nora.

Nora had a younger brother James Gahagan; his birthdates range from 1830-1839. He first shows up in the Randolph New York census in 1880 with a wife and 3 children. His obituary states he came from County Tipperary. He died at the home of a great aunt in Randolph, New York in 1927.

Any pointers on where to go from here as far as tracking Patrick Corbett in Ireland would be appreciated.