Bainbridge Island, Washington. Bainbridge Island is a city in Kitsap County, Washington, United States, and is coextensive with the eponymous island in Puget Sound. The population was 23,025 at the 2010 census, making Bainbridge Island the second largest city in Kitsap County. In July 2005, CNN/Money and Money magazine named Bainbridge Island the second-best place to live in the United States. In August 2013, Bainbridge Island was recognized by Google with an eCity Award. This award recognizes the strongest online business co