Clay Center, KS has a population of 4,193 and is the 7,234th largest city in the United States. The population density is 1,349 per sq mi which is 3745% higher than the Kansas average and 1389% higher than the national average. The median age in Clay Center is 42 which is approximately 17% higher than the Kansas average of 36. In Clay Center, 69% of the population over 15 years of age are married, 97% speak English and 0% speak Spanish. 69% of Clay Center residents were born in Kansas, 29% were born out of state, 0% were born outside of the United States and 2% were foreign born.