I have the McGannon family that married into my family with Mary Jane McGannon and John Blackwell. Mary Jane's Grandfather and Grandmother was Darby McGannon who married Mary Sallie Cogswell. Her Father and Mother were John McGannon and Mary "Polly" Carney. They were married in Jennings on Oct 14 - 1824. Photos of them are on my website along with the tombstone of Darby McGannon who fought in the Revolutionary War.
I have a number of McGannons listed.They start in 1725 in Belfast, Ireland.
The website is www.blackwellgenealogy.com The McGannon page is www.blackwellgenealogy.com/mcgannon1.htm