Forsyth is a city in and the county seat of Rosebud County, Montana, United States. The population was 1,777 at the 2010 census. Forsyth was established in 1876 as the first settlement on the Yellowstone River, and in 1882 residents named the town after General James William Forsyth who commanded Fort Maginnis, Montana during the Indian Wars and the 7th Cavalry at the Wounded Knee Massacre.