The 66th Illinois Veteran Volunteer Infantry Regiment (Western Sharpshooters) originally known as Birge's Western Sharpshooters and later as the "Western Sharpshooters-14th Missouri Volunteers", was a specialized regiment of infantry sharpshooters that served in the Union Army during the American Civil War. The regiment was intended, raised, and mustered into Federal service as the Western Theater counterpart to Army of the Potomac's 1st and 2nd United States Volunteer Sharpshooters ("Berdan's Sharpshooters").