The .22 ILARCO / 5.7x24mmRF, also known as the .22 Winchester Short Magnum Rimfire or .22 American,[2][3] was a rimfire cartridge designed in 1987 for the American-180 rimfire submachine gun.

At the time the cartridge was created, the design of the American-180 had been taken over by the Illinois Arms Company, Inc., hence the ILARCO name.

Sometime after the Illinois Arms Company, Inc. (ILARCO) purchased the rights to the American-180 they determined a more powerful cartridge would be appropriate, which resulted in the creation of the .22 ILARCO.

The new cartridge was designed so that a simple change of barrel was all that was required to switch between standard .22 Long Rifle, for which the gun was designed, and the new cartridge.

The .22 ILARCO uses a shorter version of the .22 Winchester Magnum Rimfire case, which use the same 40 gr (2.6 g) projectile as the original .22 Winchester Magnum Rimfire cartridge.