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 anomalies 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.
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Residents in county islands may resist annexation for a variety of reasons. Generally, people living on county islands have agricultural livelihoods which could come under threat if they incorporated; the risk of eminent domain seizure of their land is greater should they incorporate into a sprawling city that is quickly filling up all available land for development. Other times, the real estate of a county island is owned by one or a small number of owners who live elsewhere, and have no interest in annexation, or who intentionally hold onto the land inside a growing metropolitan area for the interest of land value going up drastically.
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.
County islands are a common feature of the fast-growth communities in fast growing areas with incorporated communities such as the Phoenix and Tucson metro areas. By law, 51% of landowners in an area as well as the city must approve annexation before it can take place.
The city of Glendale, Colorado, is one of two areas belonging to Arapahoe County, but surrounded by the City and County of Denver. The other such area, without a well-established name, is located just east of I-25 between Yale Avenue and Hampden Avenue. According to the definition established in the article, Glendale is not precisely a county island because it is a city in its own right. However, the other surrounded area is a county island.
At the county level, both of these areas are true exclaves because they are portions of one county surrounded by another county.
Memphis surrounds the Bridgewater area of Shelby County, Tennessee, with I-40 as a north boundary, Whitten Rd. as a west boundary, Shelby Farms Park as a south boundary, and roughly Appling/Cordova Rd as an east boundary. Memphis attempted to annex the entire area in the 2000s but decided to hold off because of a lack of funding and annexed only the portion between Appling Rd. and Germantown Pkwy.