Key Center, WA has a population of 3,532 and is the 8,006th largest city in the United States. The population density is 242 per sq mi which is 150% higher than the Washington average and 167% higher than the national average. The median age in Key Center is 45 which is approximately 20% higher than the Washington average of 38. In Key Center, 65% of the population over 15 years of age are married, 96% speak English and 1% speak Spanish. 57% of Key Center residents were born in Washington, 39% were born out of state, 1% were born outside of the United States and 3% were foreign born.