For the United States Air Force use of this facility, see Duluth Air National Guard Base. Duluth International Airport is a city-owned public-use joint civil-military airport located five nautical miles (9 km) northwest of the central business district of Duluth, a city in Saint Louis County, Minnesota, United States. It serves the Twin Ports area, including Superior, Wisconsin. Mostly used for general aviation but also served by three airlines, it is Minnesota's third-busiest airport, behind Minneapolis–St. Paul International Airport (MSP) and Rochester International Airport. The Minnesota Air National Guard's 148th Fighter Wing, equipped with F-16C Fighting Falcons, is based at Duluth Air National Guard Base, which is located on the grounds of the airport. Aircraft manufacturing company Cirrus is also based on the airport grounds, where it has its main manufacturing facility and headquarters. History The City of Duluth purchased the original property for the airport in 1929 from Saint Louis County. The airport was constructed on of land with two sod runways. In 1930, the airfield was dedicated as Williamson–Johnson Municipal Airport. In 1940, Northwest Airlines began the first regularly scheduled air service to Duluth. Two years later, operations were temporarily halted by World War II. In 1942, three runways were paved. Each runway was long, wide, and at nearly equal angles from each other, 30, 90, and 130 degrees. They were identified as runways 3–21, 9–27, and 13–31, respectively. The Corps of Engineers extended Runways 9–27 and 3–21 to in 1945. In 1951, the USAF extended Runway 9–27 to with a overrun and the control tower was built. Runway 9–27 was rebuilt in 1956 and extended in 1966 to in length. The original terminal building was built in 1954, south of Runway 9–27 and west of Runway 3–21. The terminal floor area was with 280 parking spaces. It would serve the airport for nearly 20 years. In 1961, the Duluth Airport Authority Board renamed the facility Duluth International Airport. In 1973, a new Terminal Building and U.S. Customs, International Arrivals Building, were completed east of Runway 13–31 and opened for operation. Runway 13–31 was shortened to to accommodate construction of an addition to the International Arrivals building. This resulted in Runway 13–31 being closed as a runway due to obstructions. Runway 13–31 was re-striped in 1980, decreasing its width to , for use as a taxiway. In 1989, the newer terminal building and the adjacent structures were connected