The 556th Strategic Missile Squadron (551 SMS) is an inactive United States Air Force unit.
 It was last assigned to the 820th Strategic Aerospace Division, stationed at Plattsburgh AFB, New York.
The 818th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Strategic Air Command at Lincoln Air Force Base, Nebraska, where it was inactivated on 25 March 1965.
The 810th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Strategic Air Command (SAC), assigned to Fifteenth Air Force at Minot Air Force Base, North Dakota, where it was inactivated on 30 June 1971.
The 813th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Fifteenth Air Force at Malmstrom Air Force Base, Montana, where it was inactivated on 2 July 1966.
The 819th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Second Air Force of Strategic Air Command (SAC) at Dyess Air Force Base, Texas, where it was inactivated on 2 July 1966.
The 18th Strategic Aerospace Division is an inactive United States Air Force unit.
 Its last assignment was with the Fifteenth Air Force at Fairchild Air Force Base, Washington, where iIt was inactivated on 2 July 1968.
The 816th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Second Air Force at Altus Air Force Base, Oklahoma, where it was inactivated on 1 July 1965.
The 825th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Strategic Air Command (SAC), assigned to Second Air Force at Little Rock Air Force Base, Arkansas, where it was inactivated on 1 January 1970.
The 820th Strategic Aerospace Division is an inactive United States Air Force organization.
 Its last assignment was with Strategic Air Command (SAC)'s Eighth Air Force at Plattsburgh Air Force Base, New York, where it was inactivated on 25 June 1965.
Plattsburgh Air Force Base is a former United States Air Force Strategic Air Command (SAC) base covering 3,447 acres (13.7 km²) in the extreme northeast corner of New York, 20 miles (32 km) south of the Canada–United States border, located on the western shore of Lake Champlain opposite Burlington, Vermont, in the city of Plattsburgh, New York.

Question: Which Air Force Base was the last assignment for the 820th Strategic Aerospace Division and is located south of the Canada-United States border?
Answer: Plattsburgh Air Force Base