Deep River is a town in Renfrew County, Ontario, Canada. Located along the Ottawa River, it lies about 200 kilometres (120 mi) north-west of Ottawa on the Trans-Canada Highway. Deep River is opposite the Laurentian Mountains and the Province of Quebec. The name Deep River purportedly derives from the fact that the Ottawa River reaches its greatest depth of 402 feet (123 m) just outside the township. However, the Ottawa River today reaches a depth of 565 feet (172 m) in Moose Bay which is located on the Holden Lake reservoir from the Des Joachim dam, west of Deux-Rivières.

Renfrew County is a county in the Canadian province of Ontario. It straddles the west bank of the Ottawa River. There are 17 municipalities in the county.