Darby, PA has a population of 10,677 and is the 3,754th largest city in the United States. The population density is 12,677 per sq mi which is 4474% higher than the Pennsylvania average and 13892% higher than the national average. The median age in Darby is 30 which is approximately 26% lower than the Pennsylvania average of 41. In Darby, 34% of the population over 15 years of age are married, 91% speak English and 3% speak Spanish. 71% of Darby residents were born in Pennsylvania, 13% were born out of state, 1% were born outside of the United States and 16% were foreign born.