The Ninety-First Regiment, also known as the 91st Pennsylvania Volunteer Infantry, was a unit that served in the Union Army during the American Civil War. Formed in 1861, the regiment participated in several key battles, including the Battle of Gettysburg and the Battle of Antietam. The regiment was composed primarily of soldiers from Pennsylvania and was known for its bravery and commitment. It played a significant role in various campaigns, contributing to the Union's efforts to preserve the nation. The Ninety-First Regiment was mustered out in 1865 after the war concluded.