Mendon is a village in Adams County, Illinois, United States.

However, there was another Fairfield in Illinois, so the village name was changed to Mendon.

[5] According to the 2021 census gazetteer files, Mendon has a total area of 0.86 square miles (2.23 km2), all land.

Illinois Route 336 passes approximately one-half mile to the east.

26.14% of all households were made up of individuals, and 15.23% had someone living alone who was 65 years of age or older.