Find zip code of address in Walnut, CA on map. List of Zipcodes in Walnut, California; ZIP Code: ZIP Code Name: Population: Type Postcode areas of Walnut, CA are 91788, 91789, 91795. Walnut, CA information. Find zip code by address or by point doing click on map. Covid-19; Forum; Cities . Walnut, CA - Standard ZIP Codes: 91789: Walnut, CA - PO Box ZIP Codes (NO DEMOGRAPHIC DATA) 91788 91765 - Diamond Bar, CA. ZIP Codes: 91788, 91789, 91795 Area code(s): 909, 626 Population: 29172 Elevation: 561ft (171m) County: Los Angeles. Nearest Zip Codes: 91789 - Walnut, CA. Walnut, California Zip Code Boundary Map (CA) Advertisement. 91723 - Covina, CA. Toggle navigation. Zip code … Portions of zip code 91789 are contained within or border the city limits of Walnut, CA, Industry, CA, Diamond Bar, CA, Rowland Heights, CA, Pomona, CA, and West Covina, CA. Map of ZIP Codes in Walnut, California. Zip code 91789 is primarily located in Los Angeles County. Drag to change point. Search. AK: AL: AR: AZ: CA: CO: CT: DC: DE: FL: GA: HI: IA: ID: IL: IN: KS: KY: LA: MA: MD: ME: MI: MN 91792 - West Covina, CA. Zip Code 91789 Description Zip Code 91789 is located in the state of California in the Reno metro area. Exit. 91791 - West Covina, CA. 91724 - Covina, CA. The official US Postal Service name for 91789 is WALNUT, California. Address: Zip Code: Full screen.