Arnold, PA has a population of 5,019 and is the 6,457th largest city in the United States. The population density is 6,856 per sq mi which is 2374% higher than the Pennsylvania average and 7468% higher than the national average. The median age in Arnold is 41 which is approximately 1% higher than the Pennsylvania average of 41. In Arnold, 42% of the population over 15 years of age are married, 97% speak English and 1% speak Spanish. 89% of Arnold residents were born in Pennsylvania, 10% were born out of state, 0% were born outside of the United States and 1% were foreign born.