Middlesex County

Middlesex County is a county located in the Commonwealth of Massachusetts, United States, one of fourteen in the state. As of the 2020 census, the population was 1,632,002, making it the most populous county in both Massachusetts and New England and the 20th most populous county in the United States. This makes the county the most populous county on the East Coast outside of New York or Florida. Middlesex County is one of two U.S. counties (along with Santa Clara County, California) to be amongst the top 25 counties with the highest household income and the 25 most populated counties. It is included in the Census Bureau's Boston–Cambridge–Newton, MA–NH Metropolitan Statistical Area. As part of the 2020 United States census, the Commonwealth's mean center of population for that year was geo-centered in Middlesex County, in the town of Natick (this is not to be confused with the geographic center of Massachusetts, which is in Rutland, Worcester County).

On July 11, 1997, Massachusetts abolished the executive government of Middlesex County primarily due to the county's insolvency. Middlesex County continues to exist as a geographic boundary and is used primarily as district jurisdictions within the court system and for other administrative purposes; for example, as an election district. The National Weather Service weather alerts (such as severe thunderstorm warnings) continue to localize based on Massachusetts's counties.