The 15th Massachusetts Volunteer Infantry Regiment was an infantry regiment that served from the State of Massachusetts during the American Civil War from 1861-1864. A part of the II Corps of the Army of the Potomac, the regiment was engaged in many battles from Ball's Bluff to Petersburg, and suffered the tenth highest fatality rate amongst Federal regiments. The regiment was composed almost entirely of men from Worcester County, and was mustered in on July 12, 1861.