Harriett Pullman Carolan was the daughter of George Pullman, the Chicago industrialist who made his fortune building the Palace railway cars that transformed American rail travel. In 1892, she married Francis Carolan of San Francisco and moved west. Twenty years later, she acquired a hilltop in Hillsborough -- the highest point in the neighborhood, with commanding views of San Francisco Bay -- and commissioned plans from Ernest Sanson, a seventy-six-year-old Parisian architect who had never visited California and never would. Sanson's exterior was inspired by Francois Mansart's seventeenth-century designs. San Francisco architect Willis Polk served as structural engineer and construction manager, translating the Frenchman's vision into reinforced concrete and brick finished with stucco scored to resemble limestone.

The gardens were designed by Achille Duchene, France's leading landscape architect, whose work was inspired by Andre Le Notre, creator of the gardens at the Palace of Versailles, Vaux-le-Vicomte, and the Tuileries. Duchene planned miles of roadways across extensive grounds landscaped with thousands of shrubs and trees, accented by fountains and statuary. Only a fraction of the scheme was ever built. The house itself contained ninety-eight rooms: nine guest bedrooms, each with an antechamber for quiet and privacy, plus service spaces that included a kitchen with white glass tile walls and ceiling, a service elevator connecting all floors, and a butler's pantry lined with Delftware tile. Sanson had incorporated three eighteenth-century period rooms that Carolan purchased in Paris, transforming the California hilltop into something closer to a French chateau than any building had a right to be.

Carolands changed hands repeatedly after its builder's era ended. It was abandoned for twenty-five years at one point, requiring fire hoses for plumbing and portable generators for light when it was finally opened to visitors. Countess Lillian Dandini, an heir to the Remillard brick fortune, lived there for twenty-three years and tried to will it to Hillsborough as a cultural center, but the town declined, unable to afford the maintenance and ruling the proposed use inconsistent with its charter. In 1985, a security guard named David Allen Raley lured two high school students onto the property, sexually assaulted and stabbed them, leaving them in a ravine. One died. Raley was convicted and sentenced to death. The house was designated California Historical Landmark 886 in 1975, but landmark status alone could not save a building that no one seemed willing or able to maintain.

Billionaire Charles B. Johnson and his wife purchased Carolands in 2009 for $26 million, ending decades of uncertainty. By 2023, the property was appraised at $130 million. A one-hour PBS documentary, The Heiress and Her Chateau: Carolands of California, premiered on KQED in 2014 and was nominated for two Emmy Awards. The 1991 Hillsborough Designer Showhouse at Carolands had attracted 68,000 visitors, each paying $20, netting over a million dollars for charity and reigniting public interest in the house. Carolands survived not because of any one rescuer but because enough people, at enough moments, recognized that a building this extraordinary deserved one more chance. It has needed many.