Rock Island, WA has a population of 917 and is the 15,683rd largest city in the United States. The population density is 1,121 per sq mi which is 1059% higher than the Washington average and 1137% higher than the national average. The median age in Rock Island is 36 which is approximately 6% lower than the Washington average of 38. In Rock Island, 60% of the population over 15 years of age are married, 64% speak English and 36% speak Spanish. 59% of Rock Island residents were born in Washington, 20% were born out of state, 1% were born outside of the United States and 20% were foreign born.