Koshkonong is a city in Oregon County, Missouri, United States. The population was 196 at the 2020 census. Koshkonong was laid out 18…Koshkonong is a city in Oregon County, Missouri, United States. The population was 196 at the 2020 census. Koshkonong was laid out 1882, taking its name from Lake Koshkonong, in Wisconsin. A post office called Koshkonong has been in operation since 1893.