A county of Ontario, Canada.

Middlesex County is a county located in the Commonwealth of Massachusetts, United States.

Middlesex University London (legally Middlesex University and abbreviated to MDX) is a public research university based in Hendon, northwest London, England.

Middlesex County is a county located in the north-central part of the U.S. state of New Jersey, extending inland from the Raritan Valley region to the northern portion of the Jersey Shore.

Monroe Township is a township located in southern Middlesex County, in the U.S. state of New Jersey.

(informally known as MX) a coeducational, independent, and non-sectarian boarding secondary school located in Concord, Middlesex County, Massachusetts.

one of eighteen first-class county clubs within the domestic cricket structure of England and Wales.