Walnut is a city in the eastern part of Los Angeles County in the U.S. state of California. According to the 2010 census, the city had a population of 29,172, and the population was estimated to be 29,685 in 2019. 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.