What were the free states of America?

Technically they were, (usually) the northern states of the USA (north of the Ohio river). Yet, the Dred Scot decision by the USA Supreme Court really meant the entire USA was a slave nation prior to the Civil War. Dred Scot was a slave taken to a "free" state, and he argued for his freedom, but, the Supreme Court ruled that no matter where he was taken, Dred Scot was still a slave.