Pennsylvania was the first state to gradually eliminate slavery, in 1780. By 1850, there were no slaves. Another guilt induced holiday for state workers.
Several states did ‘rolling’ emancipations, those born after a certain date wold be free on the 21st birthday. Massachusetts slaves won their freedom by lawsuit. A slave sued for her freedom quoting the phrase “all men are created equal”. I don’t know if she cited the MA state constitution or the U.S. Declaration, but it worked.