John Rains House, Historic house museum in Rancho Cucamonga, United States

The John Rains House is a two-story brick structure with a flat roof built between 1860 and 1861, located in Rancho Cucamonga near Los Angeles. The building contains multiple rooms including an entry hall, parlor, bedrooms, and dining areas that function as museum spaces today.

John Rains bought the Rancho Cucamonga land grant from the Tapia estate in 1858 and built this brick house in 1860–1861. He opened California's first commercial winery, but after business failings he mortgaged the house and was murdered in 1862. His wife María Merced Williams, who had inherited the rancho from her father, lost the property in the 1870s; the site was listed on the National Register on April 24, 1973.

The site is now the María Merced Williams and John Rains House, renamed by the San Bernardino County Board of Supervisors on June 28, 2022, to honor Williams, who had inherited the rancho from her father. Rains hosted lavish parties there for local elites, and the house later became a branch site of the San Bernardino County Museum.

The house stands at 8810 Hemlock St. in Rancho Cucamonga and is a branch site of the San Bernardino County Museum, so it is visited as a historic house museum. The site was renamed the María Merced Williams and John Rains House by a Board of Supervisors vote on June 28, 2022, so look for that name on signage.

The building features an advanced cooling system for its time, with water from a nearby creek circulating through underground channels beneath the foundation. This method naturally cooled the interior spaces in the hot climate long before modern air conditioning existed.