San Bruno was known as a rural town until the 1940s when two events changed the city dramatically. First, the Tanforan horse racing track was used during WWII for the internment of American Citizens of Japanese descent before sending them off to detention camps. The Army oversaw this operation and decided to use the area west of the racetrack for the Army’s Western Region Advance Personnel Depot. Thousands of military personnel went through San Bruno on their way to and from military outposts in the Pacific. This changed San Bruno forever. Many of the military personnel decided to settle in the area upon their return to the United States.

The second event of the ‘40s that changed San Bruno was George Williams’ purchase of much of the Mills land. Williams built houses on this land for the vast number of support personnel and veterans returning from the war. Soon after the Mills Park Addition was developed by Williams, the land in the western hills of San Bruno was also developed into housing. The housing boom that took place between the 1940's and 1960’s transformed San Bruno from a town of about 6500 in 1940 to a population of over 35,000 by the mid 1960’s. Since then the population has stabilized due to a lack of available land. Currently there are about 41,000 residents in San Bruno.

Today San Bruno is known as an airport city. Mills Field was dedicated in 1927 near the sight now occupied by San Francisco International Airport, but it took many years for the airport to become the success it is today. The many other more established airports in the area, along with the short and often swampy runways made Mills Field unpopular with aviators and businesses alike until 1945 when voters approved a million bond into the improvement and expansion of the airport. Since then the airport has become one of the busiest in the world, and San Bruno has grown into an international city right along with it.