Illinois has had three capitals during its history. Which one is today almost a ghost town with fourteen inhabitants?

Kaskaskia was the first state capital from 1818 until 1819. In 1820 Vandalia replaced it, but was later replaced by the present capital at Springfield. The 1819 relocation of the capital was motivated by the more central location of Vandalia.

Kaskaskia became a vanished city, gradually disappearing under the water of the meandering Mississippi River which lapped its shores.In 1881 the Mississippi went on one of its many rampages, changed its course, moving eastward and then southwest to find its old channel. This action created an island and washed away a considerable portion of the ancient capital. Each recurring spring flood encroached further upon the site until the last vestige of Kaskaskia disappeared into the Mississippi. On the remaining portion of the island is a farming community of about 131 persons and the section is called Kaskaskia, perhaps to perpetuate the name of the city that is forever gone.

http://genealogytrails.com/ill/capitols.html

Kaskaskia has become almost a ghost town due to its location on the Mississippi river and several floods that strongly affected the city. The Flood of 1844, the biggest ever recorded on the Mississippi, led to the entire relocation of the town. The Flood of 1881 destroyed most of the place, and the Great Flood of 1993 submerged the town almost completely. By 2000, Kaskaskia had only nine residents left and was the least populous incorporated community in the State of Illinois.

https://en.wikipedia.org/wiki/Great_Flood_of_1844
https://en.wikipedia.org/wiki/Great_Flood_of_1993

The reason that Kaskaskia only has 14 residents in the 2010 census: the Mississippi River shifted course again in 1881, taking over most of the town's land, and what's left of Kaskadia is now cut off from the rest of Illinois by the Mississippi River. Although the town is technically still in Illinois, you can only reach it by land from Missouri, and it now has a Missouri ZIP code although it retains Illinois phone numbers. In effect, it's now an exclave of Illinois.

https://en.wikipedia.org/wiki/Kaskaskia,_Illinois