The family has people buried in the graveyard across the street. This is just an assumption, but they were probably one of the founding members of the town. The area just north has a lot of super expensive houses, so that was probably the residences of the farmers. I haven't been able to find any historical data on the family either. I could probably get birth and death records from City Hall or something, but yeah, riiiiight. Not with my schedule.
The old "mansion" was used as a psych hospital for a while, rumor has it that Marilyn Monroe and Joe Dimaggio spent some time there, although I can't back that up. The mansion is condemned, but is a historical landmark so it can't be torn down. The property is currently owned by Horizon Services and the other buildings are being used as a substance abuse treatment facility.
Actually, the Cronin House is the name of the alcohol rehabilitation center. The large, castle-like house next door is the historic Hermann Mohr home:
The house was built in 1899 by Herman Jasper Mohr, one of the sons of Mt. Eden pioneer Cornelius Mohr. It was designed by well-known Oakland architect Thomas Newsom.
The Sea Breezes house was converted into a sanitarium and rest home in the 1940s until it was shut down by the state for code violations. Cronin House owner Horizon Services, a nonprofit whose mission is reducing alcohol- and drug-related problems, bought the three-acre parcel of unincorporated county land in 1981.
It turns out, however, that Horizon Services is well aware of the Victorian house's rich history and has been planning a restoration of the home -- now uninhabitable -- for more than 10 years.
Most recently, about five years ago, Horizon Services, with some grant funding from the cities of Hayward and Fremont, hired an architect to look at the feasibility of renovating the building, said Keith Lewis, executive director.
The planned renovation, which hasn't yet reached the county planning level, is estimated to cost about $3 million, and would convert the interior into offices for Horizon Services and the community....
And this was in 2003.
Oh, yeah: the Cronin House of Marshall is still for sale it seems, based on some pictures