You've really thrown me a curve! I have always wondered, because the census showed him living next door to my ggrandfather, Ancil Adams, in Cumberland Co, IL, whether William Coy Adams was a younger brother to Ancil or not. Now....I'm wondering whether the census taker might have erroreously put him down as an ADAMS instead of a COY!!! I did have a photocopy of the 1850 census in which I found Ancil and William, but can no longer find it. I'll have to obtain another copy of the 1850 census and verify that it does say William Coy ADAMS, although I am sure that is what was listed.
I have been unable to trace my ggrandfather's parents, so do not know who his siblings might have been.