Walnut is a city in the eastern part of Los Angeles County in the U.S. state of California. According to the 2020 census, the city had a populatio…Walnut is a city in the eastern part of Los Angeles County in the U.S. state of California. According to the 2020 census, the city had a population of 28,430. The greater Walnut Valley is located between the steep San Jose Hills to the north and the gently sloping Puente Hills to the south. Quality housing consists of master-planned single family homes ranging in size from 1,800 to 11,200 sq ft. The city hosts a highly ranked public school system: the Walnut Valley Unified School District, which has been ranked by numerous sources as one of the top public school districts in Southern California, as well as Mt. San Antonio College.