The 1840 census for Robertson Co. TN shows these men with families living next door to each other:

George Cannon (age 20-30)
William Cannon (age 30-40)
James Cannon (age 20-30)
All probably born in Tennessee.

I am quite sure this William is my g-g-grandfather who married Malinda Ganus. He is also in the 1850 Robertson Co census. The 1860, 1870, 1880 censuses show him in Christian Co. KY.

Perhaps George and James are his brothers. William also had a sister called "Polly".

Does this family sound familiar to anyone? I haven't been able to get any further information on William's siblings or parents.