Bernalillo County, NM
Bernalillo County was founded in 1852. The largest city within its boundaries is Albuquerque. Albuquerque is the county seat as well as the highest metropolitan city in the U.S., sitting at an elevation of 5,314 feet above sea level. The area is also known as the Hot Air Balloon Capital of the world. As of 2018, the population was estimated at 678,701 - making Bernalillo the most populous county in the state of New Mexico.