The Clemens family moved to Hannibal in November of 1839,
Marshall Clemens sold his holdings in Monroe County and purchased a city block in Hannibal with a hotel on it, the Virginia House. Located at the corner of Main Street and Hill, Marshall opened a store on the premises.
See The Life of Mark Twain: The Early Years, 1835-1871 (page 13-4)
In my schoolboy days I had no aversion to slavery. I was not aware that there was anything wrong about it. No one arraigned it in my hearing; the local papers said nothing against it; the local pulpit taught us that God approved it, that it was a holy thing, and that the doubter need only look in the Bible if he wished to settle his mind—and then the texts were read aloud to us to make the matter sure; if the slaves themselves had an aversion to slavery they were wise and said nothing. In Hannibal we seldom saw a slave misused; on the farm, never.
[Autobiography of Mark Twain, page 212]