Sedgwick was born in Stockbridge, Massachusetts, daughter of Matthew Ridley (1746–1789) and Catherine Livingston (1751–1813), his second wife. Sedgwick"s mother, Catherine Livingston, was the daughter of William Livingston, governor of New Jersey.
She is also painted a watercolor-on-ivory portrait of an ex-slave who came to work for her family. Her husband"s father, Theodore Sedgwick (1746–1813), was a delegate to Continental Congress, a United States Representative, Speaker of the United States. House of Representatives, a United States Senator from Massachusetts, and a state supreme court judge. Mumbet came to live as a servant in the Sedgwick household, and Susan Sedgwick painted her portrait (watercolor on ivory).
Sedgwick"s sister-in-law was Catharine Sedgwick (1789–1867), also a novelist.
Sedgwick was one of the 139 people buried in the large circular family burial plot in Stockbridge, Massachusetts known as the Sedgwick Pie.
