Three hundred and seven. So far.

That’s the number of enslaved men, women and children who can be linked by historians to the building and staffing of the White House beginning in 1792 and lasting through the first half of the 19th century.

For years, those individuals have been remembered as an afterthought, if they’ve been remembered at all. Hidden from history, conveniently forgotten. In the White House itself, there is no mention or acknowledgment of the people who built it but were not paid. No mention of the people who worked and lived there but were not free to leave.

A new online exhibit by the White House Historical Association, a private nonprofit that sits across the street from the White House, explores that untold history. The project launched this month, “Slavery in the President’s Neighborhood,” is an effort to remind Americans of the role enslaved people played in the establishment and maintenance of the country’s most symbolic address. And, just as important, to attach names to those people and flesh out their lives and experiences.

“I like to say that the people’s house deserves a people’s history,” said Matthew Costello, a historian with the organization and assistant director of the David M. Rubenstein National Center for White House History. If that history is sometimes difficult and even wrenching, Costello said, it’s all the more important to tell.

Costello recalled learning some of that hard history as he gathered material for the project. He learned how President Andrew Jackson, while in office, purchased a young enslaved girl named Emeline, 8, to work at 1600 Pennsylvania Ave.

“I have a daughter, and so when I was reading about that, it really cuts into your core as a parent,” Costello said. “To imagine that moment when your child is taken from you.”

Researched and built over the past two years by Costello and fellow historians Lindsay M. Chervinsky and Lina Mann, the association’s online portal draws from history books, primary documents and ongoing research at presidential libraries and museums such as the National Museum of African American History and Culture.

The extensive timeline includes descriptions of the role that slavery played in presidential households and paintings and drawings that depict the lives of enslaved people. There are also revealing and disturbing artifacts such as a newspaper advertisement calling for the return of Oney Judge, an enslaved woman who escaped while working for Martha Washington.

“Absconded from the household of the President of the United States,” the notice begins before providing a physical description. “Oney Judge, a light mulatto girl, much freckled, with very black eyes and bushy black hair. She is of middle stature, slender, and delicately formed, about 20 years of age.”

Particularly powerful is an index of enslaved individuals who were associated with the White House from its inception. For the men who quarried the stone, laid the bricks and built the executive mansion, it is just their first names that are known: Abraham, Amos, Cato, George, Emanuel, Moses, Nace, Salisbury, Thomas.

Last names are known only for their owners who leased them out to work on the project.

Also listed in the index are the names of the enslaved people who served in the presidential households of George Washington, Thomas Jefferson, James Madison, James Monroe, John Quincy Adams, Andrew Jackson, Martin Van Buren, John Tyler, James K. Polk and, finally, Zachary Taylor, the last president known to have had enslaved people working in his White House.

The discovery that John Quincy Adams, a known abolitionist, had enslaved people in his presidential household surprised Chervinsky.

“Everyone thinks of him as this great abolitionist president,” she said. “What we found is that while he didn’t own enslaved people and was against slavery as a political, moral issue, the reality was much more complicated.”

The historians learned that Adams’s niece and nephew lived with him during his presidency, and they owned two enslaved people whom they brought with them to live and serve them in the White House.

“We don’t know the details of their day-to-day existence, but probably they labored for free under the roof of the great abolitionist,” Chervinsky said.

The White House Historical Association’s project was inspired in part by a speech Michelle Obama gave at the 2016 Democratic National Convention where she said, “I wake up every morning in a house that was built by slaves.”

That pronouncement sent a shock wave through many Americans who didn’t know the history of slavery at the White House. The next day, the association’s website crashed under the deluge of visitors hoping to learn more about that history.

Costello, Chervinsky and Mann worked with their colleagues and with presidential historians across the country to track down as much information as possible related to slavery in the executive mansion. They learned that Jefferson, who owned more than 600 people during his lifetime, opted to have white servants at the White House. In an 1804 letter to his son-in-law, John Wayles Eppes, Jefferson wrote, “At Washington I prefer white servants, who, when they misbehave, can be exchanged.”

But Jefferson also brought three teenage enslaved girls from his home at Monticello to the White House to serve as apprentices to his French chef. By the time he finished his two terms in 1809, 11 enslaved people had lived there, including at least two children.

Perhaps the most famous enslaved person who served in the White House was Paul Jennings. Born into the estate of James and Dolley Madison in 1799, Jennings’s life is recounted in detail on the association’s website, including a story that recasts an account of White House lore.

When Madison won election in 1808, Jennings traveled to Washington as his valet. He was also put to work by Dolley Madison as a dining room servant. Dolley Madison’s most famous act as first lady was personally saving a portrait of George Washington from the walls of the White House before it was looted and burned by British troops in 1814.

But in Jennings’s telling of his years in the White House, “A Colored Man’s Reminiscences of James Madison,” published in 1865, he remembered it differently.

“It has often been stated in print, that when Mrs. Madison escaped from the White House, she cut out from the frame the large portrait of Washington … and carried it off. This is totally false.”

According to Jennings’s account, the first lady ordered workers in the White House to remove the painting, and they secured it on their own and transported it to safety.

For Chervinsky, personal stories of the enslaved people who worked at the White House help connect this long-standing symbol of America with people who may not always have felt close ties to it.

“I think it helps to make it an American story, not just a presidential story,” she said. “For a lot of people of color or people who don’t come from families of wealth, the story of the presidents doesn’t always speak to them or their experience. Whereas if we can tell a story of all the people going through, it gives people something to hold on to . . . or a way for them to feel like they are represented.”

Although the website is accessible, the work isn’t finished. The association’s historians plan to continue adding to it as they gather and corroborate more information. They know there are stories that still have not been told, and they have asked scholars and families with ties to enslaved people at the White House to share their histories. They expect there will be more names added to the list of the men, women and children who were subjected to slavery at the White House.

So far, the number is 307.