The 1st Maryland Infantry Regiment, Potomac Home Brigade was a Maryland infantry regiment of the Union Army which was active from 15 August 1861 to December 1864 during the American Civil War. Four companies were raised in Frederick County, three companies from Washington County, and three from Baltimore. The regiment started the war on railroad guard duty, and fought at the 1862 Battle of Harpers Ferry, where it was forced to surrender. The regiment was later paroled and was stationed in Martinsburg before marching to Pennsylvania and fighting at the 1863 Battle of Gettysburg; detachments went on to fight at the Battle of New Market and the Battle of Monocacy.