The man, Vincent Dale Chappelle, 52, has the mental capabilities of a 10-year-old, according to Police Lt. Rich Lawhead.
Chapelle is a white 5-ft-5, 160-pound male with hazel eyes and brown-gray hair.
He was last seen wearing a white T-shirt, gray sweatpants, black shoes and carrying a red and yellow backpack.
He was reported missing from the residence at 2 p.m. Tuesday, but might have walked away about 10 a.m., Lawhead said.
Because he recently was at a home in Yucaipa, officials are concerned he might be trying to get back there.
If anyone has information about Chapelle's whereabouts, they are asked to please contact Lawhead at 909-384-5771.