Fontana is a city in San Bernardino CountyCaliforniaUnited States. Located in the heart of the Inland Empire region of southern California, the City of Fontana is a fast-growing community known for its varied and colorful history, and for some of its important new local landmarks. It is home to several newly built landmarks, such as the largest of the San Bernardino County system libraries, a renovated historic theater, a huge new municipal park, and the Auto Club Speedway, a NASCAR racetrack located on the site of the historic Kaiser Steel Mill. Fontana is also home to the Fontana Days Half Marathon and 5K run. This race is on record as the fastest half marathon course in the world.