Surprise is a city in Maricopa County, in the U.S. state of Arizona. The population was 143,148 at the 2020 census, up from 117,517 in 201…Surprise is a city in Maricopa County, in the U.S. state of Arizona. The population was 143,148 at the 2020 census, up from 117,517 in 2010 and just 30,848 in 2000. Surprise is the spring training location of the Kansas City Royals and the Texas Rangers baseball teams.