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.
Situations which beg the surrounding city to provide emergency services to these unincorporated areas, both in their own self-interest and at the behest of those needing them.
Other problems, such as dumping and other illegal activities that occur in county islands, can prove to be a blight on the surrounding areas.
Another common kind of county islands are cemeteries, such as Greenwood Memorial Park, which is surrounded by San Diego.
Mount Greenwood Cemetery is completely surrounded by the city of Chicago but is incorporated into the neighboring suburb of Merrionette Park.
Chattanooga does not actively pursue annexation of this area as past attempts have resulted in significant landowner resistance; however, Chattanooga does allow individual landowners to voluntarily join their jurisdiction in exchange for access to city trash and police service; most residential homeowners do not consider this worth the additional 40% property tax burden.
Voluntary annexation is usually initiated by business owners within the county, one reason being to lower insurance premiums for certain commercial activities.