Surprise is a city in Maricopa County, Arizona, USA. The population was 30,848 at the 2000 census; however, rapid growth has boosted the city's population to 117,517 at the 2010 census, an increase of 281%. As such, it is the second fastest-growing municipality in the greater Phoenix metropolitan area (after Gilbert) and, between 1990 and 2000, it was the sixth fastest-growing place among all cities and towns in Arizona.The city has a 10562 sqft Aquatics Center, Maricopa County's northwest regional library, a $5.5 million, 20000 sqft library, and a 100.3 cost of living index.