The Quaker State Pennsylvania was the first to prohibit slavery in 1780, followed three years later by Massachusetts in 1783. New Hampshire also in 1783 followed a year later by Connecticut and Rhode Island. When Vermont entered the Union as the 14th state, VT entered as a Free state (1791). New York banned slavery in 1799, on which occasion Aaron Burr and Alexander Hamilton worked together. On 31 Dec 1799, the only northern state to permit slavery at this time was New Jersey; Maryland and Delaware were southern states at this time based on a slave economy (tobacco and other farming products but chiefly tobacco). Meanwhile Kentucky (1792) and Tennessee (1796) had joined as Slave states. Ohio joined as a Free state in 1802 after Tenn. The balance at that time (1803) was 8 Free and 9 Slave states, which flipped in 1804, New Jersey having finally banned slavery.
Dr. Gaius Stern