Founded as a logging town in 1858, the town is now famous for its 39 outdoor murals. This outdoor gallery has given birth to many businesses, including a theatre, antiques dealers, and eateries. The tourist industry stemming from the murals helped rejuvenate the town after its large sawmill closed in the early 1980s and was replaced by a smaller but far more efficient mill. A resident of Chemainus is known as a Chemainiac.
The name "Chemainus" comes from the native shaman and prophet "Tsa-meeun-is" (Broken Chest). Legend says that the man survived a massive wound in his chest to become a powerful chief. His people took his name to identify their community, Chemainus First Nation.
The railroad arrived in the 1880s and by the early 1920s the town's population had ballooned to 600 persons. Chemainus has no official census or municipal boundaries, so estimiates of its population today vary from approximately 3,000 to 5,000 residents.
On 13 January 2006, a Boeing 737 aircraft was sunk off the coast in order to build an artificial reef. The sinking was documented in "Sinking Wings", an episode of the Discovery Channel Series, Mega Builders.