 It was named in honor and respect of Richard Montgomery, an American Revolutionary War general killed in 1775 while attempting to capture Quebec City, Canada.The North Carolina General Assembly of 1779 named James Roper, James Allen, Cornelius Robeson, Samuel Person, and John Collier of Randolph County as the commissioners of Montgomery County and charged them with locating a county seat.In 1841 the part of Montgomery County west of the Pee Dee River became Stanly County

According to the U.S. Census Bureau, the county has a total area of , of which is land and (2.0%) is water.