San Marcos Regional Airport (ICAO: KHYI, FAA LID: HYI) is a public use airport located in Caldwell County, Texas, United States. It is four nautical miles (7 km) east of the central business district of San Marcos, a city that is mostly in Hays County. The airport is owned by the City of San Marcos and operated by Texas Aviation Partners. It is located east of the border of Caldwell County and Hays County.