McClelland was born in September 1766 in Cumberland County, Pennsylvania (later to become Bedford, afterward Westmoreland, and finally Fayette County) to Lt. Colonel John B. McClelland (1734-1782) and Martha Dale (1741-1822), near the Brown Settlement at Redstone Creek, which was referred to as Union Township at the time.
Like his father and his older brothers Hugh and Alexander, John actively participated in the American Revolutionary War [REF].