Ontario Hot Springs is a hot-water well in southern San Luis Obispo County, California, United States.

Ontario Hot Springs is about 8 mi (13 km) south of the city of San Luis Obispo along U.S. Route 101 in California.

Geographic Names Information System (GNIS), Ontario Hot Springs is located "along Gragg Canyon, 3.1 km (1.9 mi) east of the community of Avila Beach," at an elevation of 9 m (30 ft) above sea level.

[7][8] The drill struck "half a mile east of the San Luis spring, and in it a flow of gas and water similar to that in the early well had been obtained".

[9] A county history reported, "She is conducting and is the owner of Ontario Hot Springs, located on the state highway between San Luis Obispo and Pismo, on a part of the ranch owned by her father...Here Miss Budan has erected suitable buildings, and a bath house with eight tubs.

"[10] The springs, along with the Ontario Junction House, with its saloon and cabins, became a stopping point for the Hollywood crowd on their way to Hearst Castle at San Simeon, and visitors reportedly included Charlie Chaplin, W. C. Fields, and Rudolph Valentino.