The Antietam battlefield in Maryland is littered with monuments to the various regiments and companies engaged in the battle. During the Civil War units were formed from towns and regiments from States, so you would have say the 2nd Rhode Island Infantry for example. Various States erected these monuments to commemorate their dead. The practice thankfully changed after the Civil War since if a company happened to be in a particularly horrific battle a small town might lose 80% of its young men in a single day.