In the desk and filing cabinet cleaning, my wife found a letter from her Great Grandfather in Henrietta, OK to her Grandmother (his daughter) in DeWitt, AR postmarked 1984. It is literally addressed as follows, in cursive handwritten script:
Rose Cheney
DeWitt, AR - they live in new house on north part of town - it's mostly brick - got big driveway
There was no zip code, nothing else. USPS got it there just fine. The Cheney's were well known, he owned the grocery store in town. It was a letter thanking his daughter for sending some money when times were so tough, all handwritten.
Neat stuff.