Its art collection includes works by European painters Jean Béraud, Rosa Bonheur, William-Adolphe Bouguereau, Jean-Léon Gérôme, and Pierre-Auguste Renoir, landscapes by French artists of the Barbizon school, and sculptures by René de Saint-Marceaux, Alfred Barye, and Auguste Rodin.

[1] The Louis Terah Haggin Memorial Galleries and San Joaquin Pioneer Historical Museum opened its doors to the public on 14 June 1931, Flag Day.

Further, to honor her memory, Robert McKee donated funds for the building's first addition, which included storage space on the ground floor and a vestibule and large gallery on the second.

When it opened in December 1939, the room now known as the McKee Gallery contained paintings, furniture, and decorative art from the couple's New York residence, and overlooked the rose garden.

The contents were bequeathed to the museum by Miss Jennie Hunter, a local rancher, alumna of Mills College, and Daughter of San Joaquin County Pioneers, with the proviso that they be displayed just as they had been arranged in her home.

[6] Other exhibits focus on Native Americans, the Gold Rush, agriculture in the San Joaquin Valley, historic firefighting equipment, a recreated local flour mill, as well as shipbuilding and other Stockton industries.

The displays known as the Storefronts are recreations of businesses and rooms typical of establishments in San Joaquin County between 1890 and 1915, including a one-room schoolhouse and a Chinese herb shop.

Certain artists were collected in depth, however, including Jean Béraud, Albert Bierstadt, Rosa Bonheur, Jean-Léon Gérôme,[10] Edward Lamson Henry, Barend Cornelis Koekkoek, Eugène Joseph Verboeckhoven and Jehan Georges Vibert.

[1] Initially, Mrs. McKee gave the San Joaquin Pioneer and Historical Society 180 paintings, most of them part of the $10 million estate she inherited following the death of her father in March 1929.

The museum has also assembled collections of Japanese woodblock prints, illuminated manuscripts, paintings by American illustrators such as J. C. Leyendecker and Maxfield Parrish, and both Western and Asian decorative arts.

There are more than 600 archival boxes and some 100 flat files filled with photographs, maps, business records, greeting cards, advertising, and other items in the library stack room.

The history of Holt Manufacturing Company, the local industry that developed the side-hill combine harvester and the Caterpillar track-type tractor, is documented in photographs, drawings, business records, operators' manuals, and advertising.