The postmark is at the lower left. The rate of "25" cents is at the upper right, to be paid by the recipient. 25 cents was the rate for over 400 miles, thus the town name in the cancel will be quite far away from Northington, Hartford County, Connecticut, which the post office list on Jim Forte's website shows open 1810-1830, thus an uncommon destination.https://www.postalhistory.com/postoffices.asp
I agree, the cancel does seem to have "PA" at the bottom for Pennsylvania. I would look inside the letter to see how it begins. An image of the top third of the first page might be useful to us, since that usually contains a town name with the date you apparently already found. (Or look at the very end of the letter or at any notations added by the recipient.) The name of the sender can also be useful in determining an origin town. I have a guess or two for the postmark, but I will hold off until you look inside, but if you can figure out the cancel, then it can be looked up in the American Stampless Cover Catalog at:https://www.uspcs.org/resource-cent.../your-input/
The value of a stampless folded letter is quite variable. One can begin with the ASCC listing, and adjust for overall condition, the cancel quality, the noteworthiness of the sender or recipient, the interest level of the contents, the destination town, etc.