On this date in 1845 an act of Congress established consistent postal rates. Basically this act meant the mailing a letter for a distance of 300 miles or less was 5 cents per half ounce. For any distance over that it was 10 cents per half ounce. And drop letters (for local delivery) were charged 2 cents. Before that those rates were highly inflated and almost made up by the person accepting the mail.
Even though that act allowed for consistent postal rates...government postage itself was not issued until March 3, 1847. However, a postmaster could in fact issue his own stamps or stamped envelopes at the above denominations. These items are called Postmaster Provisionals. And they were only valid if used at the Post Office where they were purchased.
Interesting right? Well the more interesting part is that prepaid postage was not required until the 1850's. You could simply send a letter and the person on the other end was supposed to pay to receive it. Can you imagine if it was that way now?
After the issuance of government postage, local post offices were no longer allowed to issue provisionals. That is why they are an important but rare piece of our philatelic history.