Mill Bay is a commuter town of about 3,200 people located on Vancouver Island, British Columbia, Canada about 30 km north of Victoria, British Columbia, the capital.

Mill Bay was founded in the 1860's with lumber and milling as its primary industries, done at the mill on the bay. It is known for its ferry to Brentwood Bay on the Saanich Peninsula and the historic Malahat Drive, which is also a source of criticism due to frequent closures from either automobile accidents or weather conditions. Numerous suggestions have been made by various groups regarding a 'bypass' route (possibly a bridge), though as of 2007, the Brentwood-Mill Bay Ferry and the Malahat remain the only routes to Greater Victoria from the rest of Vancouver Island. The MV Mill Bay that has served the ferry route since 1956 is named for the town.

Brentwood College is a private high school located in Mill Bay. Frances Kelsey Secondary School is a local public high school named after pharmacologist Frances Oldham Kelsey.

The village of Shawnigan Lake is a short ten-minute drive from Mill Bay. Cobble Hill, Cowichan Bay, and Duncan are also part of the Cowichan Valley.