Mary Margaret Johnson (maiden name: Simrill) was born around 1839 in North Carolina to John Davidson Simrill and Margaret Clinton. Her father was a confectioner who owned $615 of personal property by 1860. She was baptized in Pleasant Hill Presbyterian church in Charlotte, North Carolina, in August 1839. The family settled in Chester County, South Carolina, around 1840, and she grew up there.
She married James Johnson on May 18, 1857, and they had at least two children: Isabel, born around 1868; and Mary, born around 1870. Her husband died sometime in the 1860s, and by 1870, she was living in her parents’ household in Chester County. She remained in their household until at least 1880. By 1900, she was living in her daughter Mary’s household in Gills Creek, South Carolina. She died sometime after 1920.