per wikipedia:

"In 1777, Dickinson, by then Delaware's wealthiest farmer and largest slaveholder,[19] decided to free his slaves. While the number of slaves in Kent County was not as large as the Southern Colonies and Dickinson had only 37 slaves,[19] this action has been described as requiring considerable personal courage on Dickinson's part. The strongly abolitionist Quaker influences around them likely influenced his decision,[19] and his action was facilitated by his farm's shift from farming tobacco to less labor-intensive crops, including wheat and barley.[5] Dickinson was the only Founding Father to free his slaves prior to 1786 when others also began doing so,[20] except for Benjamin Franklin, who had freed his slaves by 1770."

He was never formally a Quaker, but his family was. I didn't know Quakers owned slaves. He ONLY OWNED 37 SLAVES.

But he did the right thing in the end.