Mercer, PA has a population of 1,799 and is the 11,647th largest city in the United States. The population density is 1,580 per sq mi which is 470% higher than the Pennsylvania average and 1644% higher than the national average. The median age in Mercer is 41 which is approximately equal to the Pennsylvania average of 41. In Mercer, 52% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 82% of Mercer residents were born in Pennsylvania, 17% were born out of state, 0% were born outside of the United States and 0% were foreign born.