Which states did slavery occur in?

Answer 1

All of them, at first, north and south. The thirteen original states all had slavery when they were British colonies. Slaves were more useful in agriculture in the southern states, though, and many northerners sold their slaves to people from the south. Most of the slave ship owners, who brought the salves from Africa, were based in northern ports.

Pennsylvania, with its strong Quaker roots, was the first northern state to act to abolish slavery, even before the end of the American Revolution. But the Pennsylvania Plan was not a complete emancipation, or immediate. Any slave who was over eighteen would remain a slave until they died. Slave children would be freed when they reached the age of eighteen. Eventually this would bring an end to slavery. Most northern state adopted some version of the Pennsylvania Plan of gradual emancipation. But there were still a handful of slaves in several northern states when the Civil War ended, which were freed by the "Reconstruction Amendments" to the Constitution.

Several states considered "slave states" did not join the Confederacy. These were Delaware, Maryland, Kentucky and Missouri.

The eleven states which seceded and formed the Confederate States were South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Texas, Arkansas, Tennessee, North Carolina and Virginia.

See the "related link" below for a website with useful information about slavery in the "free" states.