The 561st Fighter Squadron is an inactive United States Air Force squadron, being last assigned to the 57th Operations Group at Nellis Air Force Base, Nevada. It was inactivated on 1 October 1996.

The 561st FS was the last United States Air Force unit to fly the F-4 Phantom II on operational missions. The last F-105 shot down in the Vietnam War was from the 561st.

The life of the 561st was resumed when the 23d Tactical Fighter Wing (the famous Flying Tigers) renumbered its squadrons the 560th, 561st, 562d, and 563d Tactical Fighter Squadrons. The 561st, 562nd and 563rd deployed to SEA in 1965, the 561st being assigned to Takhli in Thailand and Da Nang in South Vietnam. "Wild Weasel" operations became the squadron’s primary mission in mid-1970, when the squadron exchanged its F-105B/D models for F-105/Gs. On 4 April 1972 General Giap launched a three-pronged attack into South Vietnam with 200,000 troops and in April 1972, the 561st was deployed to Korat Royal Thai Air Force Base in Thailand from McConnell AFB in Kansas immediately following a mobility alert.