Marlboro is a town in Windham County, Vermont, United States. The population was 1,722 at the 2020 census. The town is home to both the Southern Vermont Natural History Museum and Marlboro Col…Marlboro is a town in Windham County, Vermont, United States. The population was 1,722 at the 2020 census. The town is home to both the Southern Vermont Natural History Museum and Marlboro College, which hosts the Marlboro Music School and Festival each summer.