The 1st Maryland Infantry, CSA was a regiment of the Confederate army, formed shortly after the commencement of the American Civil War in April 1861. The unit was made up of volunteers from Maryland who, despite their home state remaining in the Union during the war, chose instead to fight for the Confederacy. The regiment saw action at the First Battle of Manassas, in the Shenandoah Valley Campaign, and in the Peninsular Campaign. It was mustered out of service in August 1862, its initial term of duty having expired. Many of its members, unable or unwilling to return to Union-occupied Maryland, went on to join a new regiment, the 2nd Maryland Infantry, CSA, which was formed in its place.