Duncan is located in Stephens County. About 22,692 people live here (as of 2020). Between 2010 and 2020, the population declined from 23,431 to 22,692. The region is at 342 meters above sea level. The area covers about 123.6 square kilometers. There are about 858 streets in Duncan. The region was founded in 1892. The postal codes are 73533–73536. The dialing code is 580. Duncan is city and county seat of Stephens County, Oklahoma, United States. Among other things, Duncan has restaurants, supermarkets, schools and pharmacies. More information at
www.cityofduncan.com.