Buildings in downtown DeWitt, Iowa. – Farragutful, CC BY-SA 4.0 – Wikimedia Commons DeWitt is located in Clinton County. About 5,514 people live here (as of 2020). Between 2010 and 2020, the population grew from 5,322 to 5,514. The region is at 216 meters above sea level. The area covers about 15.5 square kilometers. There are about 195 streets in DeWitt. The postal codes are 52742. The dialing code is 563. DeWitt is city in Clinton County, Iowa. Among other things, DeWitt has hotels, restaurants, museums, schools, dentists and pharmacies. More information at www.cityofdewittiowa.org.