Markham, IL has a population of 12,633 and is the 3,284th largest city in the United States. The population density is 2,337 per sq mi which is 951% higher than the Illinois average and 2480% higher than the national average. The median age in Markham is 38 which is approximately 1% higher than the Illinois average of 37. In Markham, 40% of the population over 15 years of age are married, 92% speak English and 7% speak Spanish. 76% of Markham residents were born in Illinois, 20% were born out of state, 0% were born outside of the United States and 4% were foreign born.