Bainbridge Island is a city and island in Kitsap County, Washington, United States. It is located in Puget Sound. The population was 24,825 at th…Bainbridge Island is a city and island in Kitsap County, Washington, United States. It is located in Puget Sound. The population was 24,825 at the 2020 census, making Bainbridge Island the second largest city in Kitsap County.