Mill Bay is a census-designated place (CDP) in Kodiak Island Borough, Alaska, United States.

It was first listed as a CDP prior to the 2020 census.

Mill Bay is located at the northeast tip of Kodiak Island, surrounding the small bay for which the community is named.

It is bordered to the southwest by the city of Kodiak.

According to the United States Census Bureau, the Mill Bay CDP has a total area of 3.61 square miles (9.35 km2), of which 3.44 square miles (8.92 km2) are land and 0.17 square miles (0.43 km2), or 4.62%, are water.