Arnold, PA has a population of 5,090 and is the 6,345th largest city in the United States. The population density is 6,953 per sq mi which is 2349% higher than the Pennsylvania average and 7575% higher than the national average. The median age in Arnold is 41 which is approximately 1% higher than the Pennsylvania average of 40. In Arnold, 40% of the population over 15 years of age are married, 95% speak English and 1% speak Spanish. 85% of Arnold residents were born in Pennsylvania, 11% were born out of state, 2% were born outside of the United States and 3% were foreign born.