She was born in Lexington, Kentucky. Her father was Robert Smith Todd and her mother was Eliza Parker. Her parents were prominent residents of the city. Mary's paternal great-grandfather, David Levi Todd, was born in County Longford, Ireland, and emigrated through Pennsylvania to Kentucky. Her great-great maternal grandfather Samuel McDowell was born in Scotland, and emigrated to Pennsylvania. Other Todd ancestors came from England. When she was around twenty years old, Mary came to Illinois where her sister Elizabeth lived. There she met Abraham Lincoln. He was a young lawyer at that time.