Illinois 203 could refer to: Illinois Route 203, a state highway, formerly part of Illinois Route 3 and U.S. Route 66, near St. Louis School districts Elwood Community Consolidated School District 203 in Will County Naperville Community Unit School District 203 in DuPage County New Trier Township High School District 203 in Cook County O'Fallon Township High School District 203 in St. Clair County Orangeville Community Unit School District 203 in Stephenson County Vandalia Community Unit School District 203 in Fayette County Westmer Community Unit School District 203 in Mercer County