Meridian is a city located in Ada County in the U.S. state of Idaho. As of the 2010 census, the population of Meridian was 75,092 making it the third largest city in Idaho after Boise and Nampa. A 2015 estimate placed the population at approximately 90,739. Meridian is the state's fastest-growing city, with an 81.5 percent increase in population since 2000.