Collinsville is a rural unincorporated community in Solano County, California, United States. It is located at the mouth of the Sacramento River, on the north side of the river where it debouches into the Suisun Bay.[1] Collinsville is effectively separated from the more intense urban development in Contra Costa County immediately across the river, as no bridge exists connecting the two areas. The area was once proposed for a major chemical plant of the Dow Chemical Company in the 1980s.[2] The community is in ZIP code 94585 and area code 707.