Dane County Regional Airport-Truax Field is a public airport located in Madison, Wisconsin, USA. It is the largest airport in southern Wisconsin and the second busiest airport in the state. The airport is owned and operated by the Dane County Airport Commission, a public body appointed by the Dane County Board of Supervisors.

The airport has a long and interesting history. The airport began as an airfield in 1918, when a group of local aviators formed the Madison Flying Club and acquired a tract of land near the University of Wisconsin-Madison campus. The group built the first hangar and runway at the site, and the airport was officially dedicated in July 1919.

In 1920, the airport was renamed Truax Field in honor of Captain Charles Truax, a pioneering aviator and World War I flying ace who was killed in battle in France. The airport was expanded in the 1930s and 1940s, and it became a major airfield for military and civilian aircraft during World War II. In 1950, the airport was taken over by the Dane County Airport Commission, and the name was changed to Dane County Regional Airport-Truax Field.

The airport code of MSN was determined by the International Air Transport Association (IATA) in 1957. The code was derived from Madison, the largest city in the state of Wisconsin.

Today, the airport is a major hub for air travel in the region, with an average of 140 flights per day. The airport is served by several major airlines, including Delta Air Lines, American Airlines, United Airlines, Air Canada, Alaska Airlines, Southwest Airlines, and Frontier Airlines.

The airport has undergone numerous renovations and expansions over the years, including a new terminal building in 1987 and a new Air Traffic Control Tower in 1994. In 2013, the airport added a new parking garage and an automated parking system.

Dane County Regional Airport-Truax Field is an important part of the local aviation industry, providing an important gateway to the region and the state of Wisconsin. It is a vital part of the local economy and serves as an important transportation hub for the region.