William Sewall was born on 17 January 1797 in Augusta, Maine. He left home at the age of twenty-one, teaching school in Maryland and Virginia. Following his 1821 wedding to Elizabeth Ward Middleton Adams (1795–1874), Sewall relocated to Fauquier County, Virginia, and lived there for approximately eight years. Sewall and his family then moved to Illinois, where he continued to teach school and was active in the Presbyterian Church.