The 15th Massachusetts Infantry Regiment was a Massachusetts regiment of the Union Army that was active from 12 July 1861 to 26 July 1864 during the American Civil War. The regiment was raised from the men of Worcester County, and it was attached to the Army of Northern Virginia from the Battle of Ball's Bluff to the Siege of Petersburg, suffering 50% losses amid a Confederate flank attack at the Battle of Antietam and again suffering heavy losses at the Battle of Gettysburg. Most of the regiment was captured at the Battle of Jerusalem Plank Road, and the parolees were mustered out in July 1864.