James R. Reid was born in 1849 in Dundas County, Ontario, Canada, to Samuel and Nancy (Marlin) Reid. His father was an Ulster Scot born in County Londonderry, Ireland, and his mother was an Ulster Scot born in County Antrim, Ireland. His mother was born in 1812, and emigrated to Canada in 1828. Samuel and Nancy married in 1835, and Samuel died in 1860. Reid was one of 11 children, only seven of which survived into adulthood. Nancy Reid lived, never remarrying, until 1908.