There's a Martin Gannon (son of Martin and Mary) in the 1871 census of Low, Ottawa West, Quebec, Canada, age 22 (i.e. born 1849). He is the oldest of 8 children, all born in Quebec. His parents, ages 54 and 52, were born in Ireland. There is just this one Gannon family in the area at that time.
In the 1940 census, Catherine is living with two daughters and their husbands in Long Beach, Pope County, Minnesota.