The total value of ranches, farms, hunting land and other rural land and acreage for sale in San Diego County, California, recently on Land.com was approximately $1 billion. This represents 100,000 acres of farms and ranches for sale in San Diego County. San Diego County ranks fifth out of 58 counties in the Golden State for the total number of acres of land currently advertised for sale. Among cities in San Diego County with land and rural real estate for sale, Fallbrook had the most land for sale. San Diego County is one of the ten largest counties in California (4,525 square miles). It's located in the San Diego County California region of the state.