Attleboro is a city in Bristol County, Massachusetts, United States. It was once known as "The Jewelry Capital of the World" for its many jewelry manufacturers. According to the 2020 census, Attleboro had a population of 46,461. Attleboro is the fourth-largest municipality in Bristol County, behind New Bedford, Fall River, and Taunton. It became a city in 1914 after being a town for over 200 years.