On 1 July 1971, to commemorate the inauguration of the United States Postal Service, a stamp was issued with first day of issue ceremonies in every post office in the United States. Quantities of envelopes were supplied to each post office and patrons were allowed to purchase stamps and affix them to these envelopes. Then then were handed over to the clerk who applied the cancel and returned them to the customer. The resulting envelope became an official first day cover and a souvenir of the occasion.
Naturally, smaller post offices produced many fewer first day covers than did post offices in major cities. The cover pictured above is rare in that few covers with made with the Herndon Post Office cancel, Herndon, Northumberland County, Pennsylvania.