Isam Dart (1858–October 3, 1900), also known as Isom, was a cattle driver, rancher, and horse and cattle rustler during the late 19th century in the Wild West. He settled in Browns Park in northwestern Colorado, where he was considered by his neighbors to be a "superlative rider and roper, a good neighbor, and an expert and industrious cattle thief." He and his partner Mat Rash were gunned down in separate events and were believed to have been assassinated by Tom Horn, a hired gunman.