- Osan City is a city located in Gyeonggi Province, South Korea. It is part of the larger Osan Metropolitan area and is situated approximately 35 kilometers south of Seoul, the capital of South Korea. Osan City is known for its strategic location, as it is home to the Osan Air Base, which is operated by the United States Air Force. The city has a population of around 100,000 people and is a popular residential area for both South Koreans and foreign military personnel. Osan City offers a mix of urban conveniences and natural beauty, with attractions such as Osan Market, Osan Museum, and the scenic Osan Mountain.