Nancy is the oldest known child of David Fairman and his wife Suzanna. She was a granddaughter of two United Empire Loyalists; John Fairman, Sr. and William Robertson.
According to descendant Peter Johnson, Nancy may have had an illegitmate daughter Maryann Fairman (1833-1911) well before her marriage to John Barnum. That daughter married R. B. Maybee. The location, circumstances and timing fit.
In the 1880 US Census for District 404, Mayville, Tuscola, Michigan, the family of the widow Nancy A. Barnum was enumerated as follows:
Dwelling #22; Family #28
Nancy A. Barnum, White, Female, 61, Widowed, Keeping house, b. Ontario, Both parents b. Ontario
George Barnum, White, Male, 23, Son, Single, House carpenter, Unemployed 4 months during the census year, b. Ontario, Both parents b. Ontario
Wallace Barnum, White, Male, 18, Son, Single, Works on farm, Unemployed 3 months during the census year, b. Ontario, Both parents b. Ontario
Amelia Barnum, White, Female, 14, Granddaughter, Single, Works at home, b. Ontario, Both parents b. Ontario