Kalkaskia, Illinois

Population: 9, the former capital of the state, the only part of the state West of the Mississippi. - Wikipedia

I found this en route to my discovery of the term micronation. This represents a geographical/political anomaly that has become progressively less important with the growth of the Internet.

... This doesn't mean micronations have gone away. Sealand, for instance, is somewhat relevant to the UK.

"Sealand occupies a structure that was created when a purpose-built World War II-era Royal Navy barge was towed to a position above Rough Sands sandbar in the North Sea and had its hold intentionally flooded. It is sited six miles (10 km) off the coast of Suffolk, England at 51°53'40"N, 1°28'57"E, and has been occupied since 1967 by family members of Paddy Roy Bates and their associates."

... More on micronations and "forgotten" nations at Footnotes to History.