Mackay, ID has a population of 455 and is the 20,136th largest city in the United States. The population density is 525 per sq mi which is 2653% higher than the Idaho average and 480% higher than the national average. The median age in Mackay is 43 which is approximately 20% higher than the Idaho average of 36. In Mackay, 57% of the population over 15 years of age are married, 99% speak English and 1% speak Spanish. 70% of Mackay residents were born in Idaho, 30% were born out of state, 0% were born outside of the United States and 0% were foreign born.