Decker Island is a small island in the Sacramento-San Joaquin River delta, in California. It is part of Solano County. Its coordinates are 38°05′26″N 121°43′09″W / 38.0904745°N 121.7191214°W / 38.0904745; -121.7191214 (Decker Island). Part of the island is the Decker Island Wildlife Area, operated by the California Department of Fish and Wildlife.