Finding captive residents* in Industry

Reading up on Industry, with dreams of the NFL floating through my head, I came across a Wall Street Journal article from June 9, 1960 about small communities, especially dairy farmers, who were incorporating to protect themselves.
"...And two years ago, when a group wanting to carve a factory community out of the county had trouble getting the necessary 500 signatures, they visited the local mental institution, got enough inmates to sign their petitions and thus formed the City of Industry. A new law now requires such petitions be signed by qualified voters."
* UPDATE:Frank Girardot found another article on this, on the city's own Web site, albeit a Tribune story: " "Industry's" Incorporation came after a Superior Court decision denied a protest supported by residents in neighboring cities that 173 mental patients in a private santarium shouldn't be counted as inhabitants, giving proponents the nneccessary 500 population needed to incorporate."