5 digit Zip Codes - Mr Zip! are 1963.
I've seen on line that City codes began in WW2 but with under 100 people, Thompson Falls Montana couldn't have had six postal delivery zones .
[URL]https://en.wikipedia.org/wiki/Thompson_Falls,_Montana[/URL]
So I don't know what the Zone 6 is??
In Philadelphia my understanding is the zip codes incorporate the city code at the end. So Philadelphia 1, became 19101.
Then there's US Postal History page that doesn't show any year in the 20th century with 1 cent 1st class postage. ????
So another mystery.
Thank you!
At least we know it was mailed 1916 or later.
Would a small envelope have been considered post card rate?