Gardner, KS has a population of 20,667 and is the 2,098th largest city in the United States. The population density is 2,031 per sq mi which is 5689% higher than the Kansas average and 2142% higher than the national average. The median age in Gardner is 31 which is approximately 13% lower than the Kansas average of 36. In Gardner, 64% of the population over 15 years of age are married, 94% speak English and 3% speak Spanish. 57% of Gardner residents were born in Kansas, 39% were born out of state, 1% were born outside of the United States and 4% were foreign born.