The 91st Pennsylvania Volunteer Infantry was a regiment that served in the Union Army during the American Civil War. Organized in 1861, it was part of the Pennsylvania state militia and played a significant role in various battles throughout the war, including the Battle of Gettysburg. The regiment was known for its bravery and discipline, participating in key campaigns such as the Overland Campaign and the Siege of Petersburg. It was mustered out in 1865 after the war ended, having contributed to the Union's efforts to preserve the nation.