A county island is an unincorporated area within a county, usually, but not always, surrounded on all sides by another incorporated area, such as a city. On maps, these geopolitical anamolies will form jagged or complex borders and 'holes' in the city limits. Generally found more frequently in the western United States, county islands form in areas of expansion when previously smaller cities will annex and incorporate more land into their jurisdiction. If residents or landowners in a particular unincorporated area do not vote to incorporate with the surrounding city, the area remains unincorporated. The formation of a county island usually follows stages where it will come into being on the edge of an incorporated area, and as more territory is incorporated, be cut off from the rest of the unincorporated area within the county. These areas are not, by definition, exclaves because they are simply unincorporated within a surrounding city.
Because these patches of land are not incorporated into the city surrounding them, they usually fall under the jurisdiction of the county in which they are located. This can create problems if a county island is itself densely populated; they must rely on the parent county for services such as waste management, fire coverage and protection, as well as police: only county police have jurisdiction within county islands. It is under debate frequently if the surrounding city should provide emergency services to these unincorporated areas. Other problems, such as dumping and other illegal activities that occur in county islands, can prove to be a blight on the surrounding areas.
At the county level, both of these areas are true exclaves because they are portions of one county surrounded by another county.