The daughter of Eliza Parker and Robert Smith Todd, Mary was born on December 12, 1813, in Lexington, Kentucky. Her parents, pioneer settlers of Kentucky, were local aristocrats, and while she was growing up, she enjoyed a spirited social life and a private education. She loved dancing, fine clothes, and riding horses. She came in contact with politicians at an early age. Her family was well acquainted with Henry Clay, a famous American statesman who ran for president in 1832, when Mary was fourteen.
After she turned sixteen, Mary moved to Springfield, Illinois, to stay with her married sister, Ninian. Springfield became the state capital at about the same time, and it offered a lively social scene that she enjoyed. She also seemed to be husband-hunting, and she was courted by several suitors, including Stephen Douglas - the man her future husband, Abraham Lincoln, would later face in races for the senate and for the presidency.