CHATEAULIN, an arrondissement in the department of Finisterre, in France. It is 775 square miles in extent, comprising seven cantons, fifty-nine communes, and a population of 82,432 persons. The chief place, of the same name, is a city situated on the banks of the Aulne. The city itself is small, and contains not more than 100 houses, but the parish is large, and the whole has 3172 inhabitants, who partly depend on the fishery for their occupation, and partly on some slate quarries near them.