Diamond, IL has a population of 2,733 and is the 9,290th largest city in the United States. The population density is 1,448 per sq mi which is 552% higher than the Illinois average and 1499% higher than the national average. The median age in Diamond is 30 which is approximately 20% lower than the Illinois average of 37. In Diamond, 58% of the population over 15 years of age are married, 94% speak English and 6% speak Spanish. 84% of Diamond residents were born in Illinois, 14% were born out of state, 0% were born outside of the United States and 2% were foreign born.