The Free Public Library of Petaluma (also Old Carnegie Library, Carnegie Free Library and Petaluma Historical Library and Museum) is a research library and history museum at 20 Fourth Street in Petaluma, Sonoma County, California, US. Built in 1904 as a Carnegie Free Library, it was designed by Brainerd Jones as his first major commission before the architect gained regional recognition. In the 1970s, it was re-purposed as a research library and historical museum. The building is listed on the National Register of Historic Places.