For more than 200 years, slave-based tobacco plantations dominated the economy of Prince George's County, and after the county seat moved from Mount Calvert to Upper Marlboro in 1721, Mount Calvert became the center of a large tobacco plantation. The brick plantation house was built by John Brown in 1789. Enslaved African-Americans tended livestock, planted and harvested tobacco and other crops, and worked as servants and craftsmen at Mount Calvert throughout its history as a plantation. Their numbers ranged from 27 in 1799 to 51 in 1864, and although most of their names are unknown today, it is known that in 1864 the children of Charity Jackson, Chrstianna Harrison, Martha Crauford, and Sarah Brent lived there. Following the Civil War and freedom, African-Americans continued to live and work at Mount Calvert as laborers, servants, and tenant farmers. Archaeologists have discovered evidence of slave quarters there, and artifacts such as ceramics, pipe stems, and historical documents help fill gaps in the history of the enslaved and free African-Americans who lived and worked at Mount Calvert.