Ellsworth Air Force Base (AFB) (IATA: RCA, ICAO: KRCA, FAA LID: RCA) is a United States Air Force (USAF) base located about 10 miles (16 km) northeast of Rapid City, South Dakota, just north of the town of Box Elder.

The host unit at Ellsworth is the 28th Bomb Wing (28 BW). Assigned to the Global Strike Command's Eighth Air Force, the 28 BW is one of the USAF's two B-1B Lancer wings, along with the 7th Bomb Wing at Dyess AFB, Texas. In 2023, the 28th Bomb Wing is commanded by Colonel Derek Oakley; its command chief master sergeant was Chief Master Sergeant Adam Vizi.

Ellsworth has a population of about 8,000 military members, family members and civilian employees. Rapid City itself has a population of 78,824. There are about 3,800 military retirees in western South Dakota.

For decades, Ellsworth's main entrance included a symbolic B-52 Stratofortress, a gift from the citizens of Rapid City. This entrance has recently been replaced.

An expansion of a bomber training area encompassing the Northern Plains known as the Powder River Training Complex began in 2008.