CHATEAU-SONTIER, an arrondissement of the department of the Mayenne, in France, the extent of which is 375 square miles. It is divided into six cantons, and these into seventy-nine communes, containing 66,849 inhabitants. The chief place is a city of the same name, situated on the river Mayenne, which is navigable to a certain extent; and it contains 700 houses, and 4834 inhabitants, who manufacture linens, serges, eslamines, hats, and leather. It is in long. 0. 51. W., and lat. 47. 47. N.