completely unrelated (or so I thought) Backus family search. Turns out that
Laura's step-mother was Sarah (Whiting) Backus, ex-wife of John Backus. Sarah
married 2nd, Thomas Ingersoll, who was Laura (Ingersoll) Secord's father. As a Mayflower descendant of John Alden, Sarah's marriages are found at the Descendants of John Alden website.
From The Ingersolls of Hampshire : a genealogical history of the family from their settlement in America, in the line of John Ingersoll of Westfield, Mass.:
Thomas [Ingersoll, Laura Secord's father], born March 24, 1750. Emigrated to Canada before the Revolutionary War*. Settled the town of Ingersoll. Served as a major in the Colonial troops. Married three times : (1) Elizabeth Dewey, 1775 ; (2) Mrs. Mercy Smith, 1785 ; (3) Mrs. Sarah Backus, 1789-
The Ingersoll and Backus families lived in Great Barrington, Massachusetts (that is where the divorce between John Backus and Sarah Whiting Backus took place).
*Henry Knox and the Revolutionary War Trail in Western Massachusetts, stated that Thomas Ingersoll went to Canada in 1792. Also stated "Laura was four months old when Henry Knox's oxen caravan went past her family's house in Great Barrington."