Châteaulin (French: [ʃɑtolɛ̃] ; Breton: Kastellin) is a commune in the Finistère department and administrative region of Brittany in north-western France. It is a sub-prefecture of the department.

Châteaulin is in a valley towards the center of Finistère on the River Aulne and the Canal de Nantes à Brest, mid-way between Quimper to the south and Brest to the north. To the west the Menez-Hom hills separate it from the Crozon peninsula and the Bay of Douarnenez, which opens into the Atlantic Ocean.

In French the inhabitants of Châteaulin are known as Châteaulinois.

Historical population

Year Pop. ±% p.a. 1793 2,514 —     1800 3,172 +3.38% 1806 3,161 −0.06% 1821 2,426 −1.75% 1831 2,783 +1.38% 1836 2,968 +1.30% 1841 2,548 −3.01% 1846 2,790 +1.83% 1851 2,849 +0.42% 1856 2,852 +0.02% 1861 2,892 +0.28% 1866 3,259 +2.42% 1872 3,339 +0.41% 1876 3,436 +0.72% 1881 3,462 +0.15% 1886 3,656 +1.10% 1891 3,677 +0.11% 1896 3,857 +0.96%	Year Pop. ±% p.a. 1901 3,874 +0.09% 1906 4,237 +1.81% 1911 4,271 +0.16% 1921 4,005 −0.64% 1926 3,766 −1.22% 1931 3,615 −0.82% 1936 3,702 +0.48% 1946 3,954 +0.66% 1954 3,958 +0.01% 1962 4,096 +0.43% 1968 4,370 +1.09% 1975 4,711 +1.08% 1982 5,357 +1.85% 1990 4,965 −0.95% 1999 5,157 +0.42% 2007 5,298 +0.34% 2012 5,181 −0.45% 2017 5,214 +0.13%
Source: EHESS and INSEE (1968-2017)

In 2008 1.96% of primary-school children attended bilingual schools.

Châteaulin's economy is based on food processing (salmon and poultry) and, to an ever-greater extent, tourism. The Gendarmerie school on the outskirts of the town provides for a large number of families and the many recruits passing through the school provide the economic backbone of the town's night-life. The cake shop Histoire de Macaron is famous for its tasty and wide range of macaroons as well as the Java, created in 1907 by Mister Le Meur, which is a legend in the town.

• Yves Marie André, better known as le Père André (1675–1764), Jesuit priest and philosopher.
• 27 November 1761 : Birth of Julien Marie Cosmao-Kerjulien (died in Brest 17 February 1825), Rear-Admiral and Baron d'Empire.
• Jean Moulin, emblem of the French Resistance during the Second World War, was the sub-prefect from 1930 to 1933.
• Henri Ernest Ponthier de Chamaillard, usually known as Ernest de Chamaillard, (9 December 1862, Gourlizon – 1931, Eaubonne) was a French artist, one of a group of painters who gathered in the Breton village of Pont-Aven. He was a friend and student of Paul Gauguin. In 1893, unable to make a living from his painting, he moved to Châteaulin behind Église Saint-Idunet where he worked as a lawyer until 1905.

Châteaulin is twinned with:

• - Clonakilty, County Cork, Ireland.
• - Grimmen, Mecklenburg-Vorpommern, Germany

• Cantons of the Finistère department
• Communes of the Finistère department
• Arrondissements of the Finistère department
• Parc naturel régional d'Armorique
• Brennilis Parish close

• Official website of the town of Châteaulin / Kastellin (in French)
• Base Mérimée: Search for heritage in the commune, Ministère français de la Culture. (in French)