Arco, ID has a population of 780 and is the 16,777th largest city in the United States. The population density is 730 per sq mi which is 3726% higher than the Idaho average and 706% higher than the national average. The median age in Arco is 41 which is approximately 15% higher than the Idaho average of 36. In Arco, 60% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 60% of Arco residents were born in Idaho, 38% were born out of state, 0% were born outside of the United States and 2% were foreign born.