Middlesex is a county in England, largely a metropolitan area of London, bounded on the north by Hertfordshire, on the east by Essex, on the southeast by County of London, on the south by Surrey, and on the west by Buckinghamshire. Its area is 382 square miles.
With the exception of Rutland, it is the smallest of English counties. It is drained by the Thames, which forms its southern border. The capital is Brentfield.