Greenfield is a city in Monterey County, California, United States. Greenfield is located in the Salinas Valley, 33 miles southeast of Salinas, at an elevation of 289 feet. The city was the fastest growing in the county during the 2000s, the population was 12,583 in 2000, increasing to 16,330 in the 2010 census. Its most well-known public event is the annual Harvest Festival. Greenfield is a member of the Association of Monterey Bay Area Governments.