Indiana, a state in the Midwest, played an important role in supporting the Union during the American Civil War. Despite anti-war activity within the state, and southern Indiana's ancestral ties to the South, Indiana was a strong supporter of the Union. Indiana contributed approximately 210,000 Union soldiers, sailors, and marines. Indiana's soldiers served in 308 military engagements during the war; the majority of them in the western theater, between the Mississippi River and the Appalachian Mountains. Indiana's war-related deaths reached 25,028. Its state government provided funds to purchase equipment, food, and supplies for troops in the field. Indiana, an agriculturally rich state containing the fifth-highest population in the Union, was critical to the North's success due to its geographical location, large population, and agricultural production. Indiana residents, also known as Hoosiers, supplied the Union with manpower for the war effort, a railroad network and access to the Ohio River and the Great Lakes, and agricultural products such as grain and livestock. The state experienced two minor raids by Confederate forces, and one major raid in 1863, which caused a brief panic in southern portions of the state and its capital city, Indianapolis.

During the American Civil War, the United States was referred to as simply the Union, also known colloquially as the North, after eleven Southern slave states seceded to form the Confederate States of America (CSA), which was called the Confederacy, also known as the South. The name the "Union" arose from the declared goal of the United States, led by President Abraham Lincoln, of preserving the United States as a constitutional federal union.