Finding a city's ZIP code is a simple process. However, you might need to know an exact address because most cities have more than one ZIP code. You can usually find all the information you need with an online search. If you don't have access to the Internet at the time, however, you can use other means to locate a ZIP code.
USPS Online Search
The simplest way to locate a ZIP code is by using the United States Postal Service website. The USPS has a simple online ZIP code locator tool. Enter the city and state and you'll get a list of possible ZIP codes. If you have an actual street address, enter that and you'll be given the exact ZIP code.
Alternative Online Searches
You can also find a city's ZIP code online without using the USPS website. Performing an Internet search for the city name, state and "ZIP code" will give you a list of websites that offer the information you're seeking. Sites such as Addresses.com or Zip-Codes.com will give you a list of ZIP codes for a particular city along with a map and the city's demographics.
USPS also offers a directory of certified vendors who can provide address and ZIP code matching offline. These vendors are certified through CASS and MASS, two systems which evaluate the proficiency and accuracy of address-matching software. The complete list of approved vendors is on the USPS website and includes companies such as AccuZip, which works with Windows; and Mail Star, which works with Linux and Windows.
Make a Phone Call
If you just need one or two city ZIP codes and you don't have Internet access, you can contact USPS directly for the information by phone. The general information line is 1-800-ASK-USPS. As of 2015, he line is open 8 am to 8:30 pm Eastern Standard Time, Monday through Friday, and 8 am to 6 pm EST on Saturdays.