James Monroe Enslaved Hundreds. Their Descendants Still Live Next Door.

Mr. Violette, a ninth-generation Virginian and Ms. Burnett, a reference librarian, started their research of the sale by asking basic questions: How many of the enslaved were sold? Did they leave Florida after emancipation? Then, after visiting Middle Oak, they wondered: Could they be related by blood to the Monroe descendants in Virginia?

The researchers pored over archival records documenting shipping manifests, property inventories, bills of sale, death certificates. In a letter to James Madison, Monroe said he had arranged to have the enslaved taken in families. At least three couples — Dudley and Eve, Toby and Betsy, Jim and Calypso — along with their children, were sent to Florida, yanking apart the larger Highland enslaved community.

“The more we were able to find, the more we knew how important it was to try to help reunite these two communities,” Mr. Violette said.

Fifteen months after Mr. Violette visited Middle Oak, he and Ms. Burnett visited another small church, this time in Florida. It was founded, in part, by children once enslaved at Highland. The researchers met about a dozen people in Monticello, including a woman whose grandfather was a descendant of Dudley and Eve, one on the enslaved couples sold to Florida, and the first direct link between the two descendant communities in Florida and Virginia.

Ms. Burnett cried as she described piecing together the life of Garrett Sanders, a son of Toby and Betsy, who was about 18 when he was sold with his parents and sent to Casa Bianca. After emancipation, he appeared in the 1870 census with his occupation listed as a blacksmith. Seven years later, he registered to vote, in 1867, and cast a ballot in the 1876 presidential election.

“It means he made it. He made it to freedom,” Ms. Burnett said. “It is an incredible discovery to find the evidence that an enslaved person was finally able to live free.”