Many of these "hidden" pieces can now be seen online.
Go to tinyurl.com/history732 to see 500 pieces from the collections. More pieces will appear as the museum marshals resources toward the effort, said museum president Mitch Postel.
"It's becoming more and more professional among museums to allow people access to the contents of their collections," Mr. Postel said. "A lot of bigger museums like the Smithsonian and the California Historical Society are doing it."
The county history museum currently features exhibits on natural resources, suburban development, ethnic experience, and entrepreneurial achievement on the Peninsula, including 15,000 three-dimensional objects. The collections date back to the times of the Ohlone Indians.
The museum holds 200,000 archival items in its research library, including photographs, books, newspapers, manuscripts, memorabilia and government records.
"We have extensive collections, especially photographic collections, that we're trying to bring to the public to give a sense of what we've got," Mr. Postel said. "Only about 5 percent of our three-dimensional items, and an even smaller percentage of our archival items, are on display."
Collections posted online include photos of and information about: the San Mateo County Sports Hall of Fame, the Charles Parsons Model Ship collection, and a sampling of James Van Court's photographs of Redwood City in the 1890s.
The history museum is open every day except Monday from 10 a.m. to 4 p.m. The research library is accessible Tuesday to Thursday from 10 a.m. to noon and 12:30 p.m. to 4 p.m., and on Sundays from noon to 4 p.m.
Visit historysmc.org or call 299-0104 for more information.