1 definition found illiopolis - U.S. Gazetteer (1990) : Illiopolis, IL (village, FIPS 37127) Location: 39.85131 N, 89.24705 W Population (1990): 934 (381 housing units) Area: 1.1 sq km (land), 0.0 sq km (water) Zip code(s): 62539