Posen, IL has a population of 6,251 and is the 5,602nd largest city in the United States. The population density is 5,347 per sq mi which is 2305% higher than the Illinois average and 5802% higher than the national average. The median age in Posen is 30 which is approximately 20% lower than the Illinois average of 37. In Posen, 47% of the population over 15 years of age are married, 62% speak English and 38% speak Spanish. 68% of Posen residents were born in Illinois, 6% were born out of state, 1% were born outside of the United States and 25% were foreign born.