Is there any place online I can find 4 digit extensions for zip codes?

[Mears]

I need to find one for an old address. Does anyone know of a site online that has a database of these?

 

[erub]

www.usps.gov

 

[mithrandir2001]

http://www.usps.com/ncsc/lookups/lookup_zip+4.html

 

[HappyFace]

There's also a city/state/zip code associations page. link

 

[Mears]

Thanks, guys. What is the +4 used for anyways? I noticed that there are multiple entries for each regular zip.

 

[mithrandir2001]

The +4 identifies your carrier route. Your zip code may service thousands of addresses, so the +4 extension saves the postal service from having to figure out which particular carrier for that post office should get the piece to deliver. It also lowers the postage cost if you do bulk mailings.