24 Hour Fitness, by membership numbers, is the largest privately owned and operated chain of fitness centers in the world. 24 Hour Fitness is also the third next to Gold's Gym and Fitness First in most popular United Kingdom Gyms. This chain operates over 400 clubs, has 4 million members in 18 states and employs more than 18,000 employees in America alone. 24 Hour Fitness also boasts a number of employees who work in the call centers in the Philippines and Spokane, Washington. Headquartered in San Ramon, California, it was founded in 1983, and was intended to be only a one-club operation.