Slave cases are still cited as good law. This team is trying to change that

State courts in every state highlighted on this map have cited cases involving enslaved people in the 1980s or later.

Citing Slavery Project, Michigan State University

This story starts — but certainly doesn’t end — in 19th century Maryland, when John Townshend updated his will.

Townshend grew convinced at the end of his life that God would punish him if he did not free the enslaved people he owned and give them all of his property. But Townshend’s relatives challenged his final wishes in court, arguing that his decision had been the result of a delusion.

That 1848 case was the first U.S. appearance of what became known as the “insane delusion rule,” which remains grounds for contesting wills to this day. And Townshend v. Townshend itself has been cited in at least 70 other cases across the country — from New Hampshire to California — over the years, as recently as 2007.

It’s one of thousands of cases involving enslaved people that lawyers and judges continue to cite as good precedent, more than a century after the 13th Amendment abolished slavery in the U.S.

Justin Simard, an assistant professor at Michigan State University’s College of Law, estimates there are about 11,000 such cases out there — and about one million more that use them to back up their arguments.

“I’ve done some analysis just with a sample of cases and concluded that 18% of all published American cases are within two steps of a slave case, so they either cite the slave case or cite a case that cites a slave case,” Simard tells NPR. “The influence is really, really extensive.”

Simard has spent years documenting them, with the help of…