President Franklin Delano Roosevelt and his WPA (Works Progress Administration) commissioned the Federal Writer’s Project to interview over 2,300 formery enslaved people in 17 states. Collected from 1936 to 1938, over 70 years after the end of slavery, these one on one interviews are considered some of the most valuable first person accounts ever collected. Here's a link to the Library of Congress page about them, Born in Slavery: Slave Narratives from the Federal Writers' Project, 1936 to 1938
The images above are pages from the collection. On the far right is the account of a man named Dennis Simms. He is described as an ex-slave who was born in 1841 on a tobacco plantation in Contee, MD in Prince George's County - only about 10 miles from where Greenbelt is now. To read his narrative, click here.