| Official Name: | Mill Bay |
| Settlement Type: | Unincorporated community |
| Pushpin Map: | Vancouver Island#Canada British Columbia#Canada |
| Pushpin Map Caption: | Location of Mill Bay in British Columbia |
| Subdivision Type: | Country |
| Subdivision Name: | Canada |
| Subdivision Type1: | Province |
| Subdivision Name1: | British Columbia |
| Subdivision Type2: | Regional District |
| Subdivision Name2: | Cowichan Valley Regional District |
| Timezone: | PST |
| Utc Offset: | -8 |
| Timezone Dst: | PDT |
| Utc Offset Dst: | -7 |
| Coordinates: | 48.6506°N -123.5592°W |
| Postal Code Type: | Postal code |
| Postal Code: | V8H & V0R 2P0 |
| Area Code: | 250, 778 |
Mill Bay is a commuter town of about 7,200 people located on Vancouver Island, British Columbia, Canada, about 30km (20miles) north of Victoria, the capital. It is part of the Cowichan Valley Regional District.
Mill Bay was founded in the 1860s with lumber and milling as its primary industries, done at the mill on the bay. It was named for the sawmill built in the area in 1861 by Henry S. Shepherd soon purchased by William Sayward. 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 best routes to Greater Victoria from the rest of Vancouver Island (a third route goes south from Lake Cowichan via Port Renfrew to Victoria). The MV Mill Bay that has served the ferry route since 1956 is named for the town but was taken out of service in 2011 and is now served by the MV Klitsa.
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 ten-minute drive from Mill Bay. Cobble Hill, Cowichan Bay, and Duncan are also part of the Cowichan Valley.
The Mill Bay Freemasons Hall meets on the third Thursday of the month and also offers room to other community organizations.