Vermont banned slavery in 1777, by 1804 all northern states had banned slavery.
Vermont was not a state of the United States in 1777. It was part of New York until, in 1777, Vermont declared its independence, seceded, and waged a successful rebellion. In so doing, Vermont became a free and independent state (aka Vermont Republic or Commonwealth of Vermont) until it joined the union in 1791. It was as an independent state or republic that Vermont did, indeed, prohibit slavery in 1777.
Vermont v. New Hampshire, 289 U.S. 593, 607-608 (1933)
Vermont was admitted to the union in 1791 as "an independent state with self-constituted boundaries."
True. I was just using 1776 as a point after which it became an issue independent of England. I suppose 1781 or 1783 could be used. Because imo, attributing slavery in the colonies pre 1776 to what has become the US is inaccurate, the colonies only “control” was whether an individual purchased a slave or not. As another poster noted a couple states attempted to abandon slavery earlier, but were overridden by England.