Rialto is a city in San Bernardino County, California, United States. The population was 99,171 with the 2010 Census.Rialto is home to four major regional distribution centers: Staples Inc., which serves stores across the entire West Coast of the United States, Toys "R" Us, Under Armour and Target in the northern region of the city, in the Las Colinas community. One of the United States' largest fireworks companies, Pyro Spectaculars, is also headquartered in Rialto.