Sibley, IA has a population of 2,667 and is the 9,434th largest city in the United States. The population density is 1,585 per sq mi which is 2802% higher than the Iowa average and 1650% higher than the national average. The median age in Sibley is 44 which is approximately 16% higher than the Iowa average of 38. In Sibley, 66% of the population over 15 years of age are married, 88% speak English and 9% speak Spanish. 60% of Sibley residents were born in Iowa, 33% were born out of state, 0% were born outside of the United States and 7% were foreign born.