Leavenworth, KS has a population of 35,948 and is the 1,172nd largest city in the United States. The population density is 1,467 per sq mi which is 4082% higher than the Kansas average and 1519% higher than the national average. The median age in Leavenworth is 35 which is approximately 4% lower than the Kansas average of 36. In Leavenworth, 54% of the population over 15 years of age are married, 93% speak English and 3% speak Spanish. 40% of Leavenworth residents were born in Kansas, 53% were born out of state, 3% were born outside of the United States and 4% were foreign born.