APA (7th ed.) Citation

United States. Post Office Dept. (1968). National Zip code directory. [Bureau of Operation.

Chicago Style (17th ed.) Citation

United States. Post Office Dept. National Zip Code Directory. Washington: [Bureau of Operation, 1968.

MLA (9th ed.) Citation

United States. Post Office Dept. National Zip Code Directory. [Bureau of Operation, 1968.

Warning: These citations may not always be 100% accurate.