Brattleboro, originally Brattleborough, is a town in Windham County, Vermont, United States, located about 10 miles north of the Massachusetts state line at the confluence of Vermont's West River and the Connecticut River. With a 2022 Census population of 12,106, it is the most populous municipality abutting Vermont's eastern border with N…Brattleboro, originally Brattleborough, is a town in Windham County, Vermont, United States, located about 10 miles north of the Massachusetts state line at the confluence of Vermont's West River and the Connecticut River. With a 2022 Census population of 12,106, it is the most populous municipality abutting Vermont's eastern border with New Hampshire, which is the Connecticut River.