Mary Abigail Marston was born around 1844 in Maine to Daniel Marston and Rosannah Dow. Her father was a merchant who owned $2,000 of real estate and $4,000 of personal property by 1860. She grew up and attended school in Phillips, Maine.
She married Walter Barnes in the 1860s, and they had at least three children: Walter, born around 1867; Lloyd, born around 1869; and Daniel, born around 1870. Her husband worked as a physician and surgeon in Phillips, and by 1870, they owned $150 of real estate and $1,000 of personal property. They eventually moved to Andover, Maine, and she died sometime after 1900.