MONTFORT, an arrondissement of the department of Ille Vilaine, in France, extending over 390 square miles, and containing a population of 56,800 persons. It is divided into five cantons and forty-six communes. The capital, of the same name, stands on the river Meu, near its junction with the Chailon. Its walls are dilapidated, and it contains only 1250 inhabitants.