Merdrignac (French pronunciation: [mɛʁdʁiɲak]; Breton: Medrigneg) is a commune in the Côtes-d'Armor department of Brittany in northwestern France.

[3] The River Meu forms most of the commune's northern border.

The average annual rainfall is 931.5 mm (36.67 in) with December as the wettest month.

The temperatures are highest on average in July, at around 17.9 °C (64.2 °F), and lowest in December, at around 5.5 °C (41.9 °F).

Inhabitants of Merdrignac are called merdrignaciens in French.