The Côtes-d'Armor (/koʊt dɑːrmər/ koht dar-mər, /-dɑːrmɔːr/ -⁠dar-mor; French pronunciation: [kot daʁmɔʁ] ; Breton: Aodoù-an-Arvor, [ˈoːdu ãn ˈarvor]), formerly known as Côtes-du-Nord until 1990 (Breton: Aodoù-an-Hanternoz, [ˈoːdu ãn ˌhãntɛrˈnoːs]), is a department in the north of Brittany, in northwestern France. In 2019, it had a population of 600,582.

Côtes-du-Nord was one of the original 83 departments created on 4 March 1790 following the French Revolution. It was made up from the near entirety of the ancient Pays de Saint-Brieuc, most of historical Trégor, the eastern half of Cornouaille, and the north-western part of the former diocese of Saint-Malo.

On 27 February 1990, the name was changed to Côtes-d'Armor: the French word côtes means "coasts" and ar mor is "the sea" in Breton. The name also recalls that of the Roman province of Armorica ("the coastal region").

Côtes-d'Armor is part of the current administrative region of Brittany and is bounded by the departments of Ille-et-Vilaine to the east, Morbihan to the south, and Finistère to the west, and by the English Channel to the north.

The region is an undulating plateau including three well-marked ranges of hills in the south. A granitoid chain, the Monts du Méné, starting in the south-east of the department runs in a north-westerly direction, forming the watershed between the rivers running respectively to the English Channel and the Atlantic Ocean. Towards its western extremity this chain bifurcates to form the Montagnes Noires in the south-west and the Monts d'Arrée in the west of the department. Off the coast, which is steep, rocky and much indented, are the Jentilez, Bréhat and other small islands. The principal bays are those of Saint-Malo and Saint-Brieuc.

The most populous commune is Saint-Brieuc, the prefecture. As of 2019, there are 6 communes with more than 10,000 inhabitants:

Commune	Population (2019)
Saint-Brieuc	43,605
Lannion	20,210
Lamballe-Armor	16,688
Dinan	14,407
Plérin	14,309
Ploufragan	11,383

The inhabitants of the department are known in French as Costarmoricains.

Historical population

Year Pop. ±% p.a. 1801 504,303 —     1821 552,424 +0.46% 1831 598,872 +0.81% 1841 607,572 +0.14% 1851 632,613 +0.40% 1861 628,676 −0.06% 1876 630,957 +0.02% 1881 627,585 −0.11% 1891 618,652 −0.14% 1901 609,349 −0.15% 1921 557,824 −0.44% 1936 532,000 −0.32%	Year Pop. ±% p.a. 1946 526,955 −0.10% 1954 503,178 −0.58% 1962 501,923 −0.03% 1968 506,000 +0.13% 1975 525,556 +0.54% 1982 538,860 +0.36% 1990 538,443 −0.01% 1999 542,398 +0.08% 2006 569,498 +0.70% 2011 594,375 +0.86% 2016 598,953 +0.15%
Graphs are unavailable due to technical issues. Updates on reimplementing the Graph extension, which will be known as the Chart extension, can be found on Phabricator and on MediaWiki.org.
Sources:

Côtes-d'Armor's long tradition of anti-clericalism, especially in the interior around Guingamp (a former Communist stronghold), has often led to the department's being seen as an area of left-wing exceptionalism in a region that historically was otherwise strongly Catholic and right-wing. The current president of the departmental council, Christian Coail, is a member of the Socialist Party.

Party groupings		seats
	Centre et droite républicaine	32
	Socialiste et républicain	15
	Communiste et républicain	5
	non-party	2

Constituency		Member	Party
	Côtes-d'Armor's 1st constituency	Bruno Joncour	MoDem
	Côtes-d'Armor's 2nd constituency	Hervé Berville	La République En Marche!
	Côtes-d'Armor's 3rd constituency	Marc Le Fur	The Republicans
	Côtes-d'Armor's 4th constituency	Yannick Kerlogot	La République En Marche!
	Côtes-d'Armor's 5th constituency	Éric Bothorel	La République En Marche!

The western part of the department is part of the traditionally Breton-speaking "Lower Brittany" (Breizh-Izel in Breton). The boundary runs from Plouha to Mûr-de-Bretagne. The Breton language has become an intense issue in many parts of Brittany, and many Breton-speakers advocate for bilingual schools. Gallo is also spoken in the east and is offered as a language in the schools and on the baccalaureat exams.

• 
  Paimpol
• 
  Perros-Guirec
• 
  Fort-la-Latte
• 
  Cap Fréhel
• 
  Castel Meur house in Plougrescant
• 
  Statue of Bertrand du Guesclin in Dinan

• Anne Beaumanoir (1923–2022), one of the Righteous Among the Nations, was born in Guildo.
• Bernadette Cattanéo (1899–1963), trade unionist and militant communist
• English-born poet Robert William Service (1874–1958), known as the "Bard of the Yukon", is buried in Lancieux.

• Cantons of the Côtes-d'Armor department
• Communes of the Côtes-d'Armor department
• Arrondissements of the Côtes-d'Armor department

• (in French) Prefecture website
• (in French) Departmental Council website
• (in French) Tourist board website