What is a First Day Cover? by Richard C. Leavitt
New stamps issued by the U.S. Postal Service (USPS) are usually offered for sale in a single city on the First Day of Issue, and then are made available for sale throughout the country after the First Day. A First Day Cover is an envelope, card or other piece of paper that has an authorized USPS cancel applied on the First Day of Issue.

Collins Hand Painted FDC

David Dube Hand Painted FDC
The First Day cancel may be an “Official” cancel denoting the City in which the stamp was issued; or it may be an “unofficial” cancel applied on the First Day of Issue, but in a city other than the official city.

Prior to 1937, the cancel applied to a First Day Cover was indistinguishable from regular cancels. In 1937, commencing with Scott # 795 (1937 Ordinance), the Postal Service applied a “First Day of Issue” cancel to “official” First Day Covers, making the task of identifying a First Day Cover a bit easier. “Unofficial” First Day Covers contain only the standard cancel mark for the unofficial city; thus the date should be checked against the “official” First Day of Issue date.

Prior to the 1930’s most First Day Covers were on plain envelopes. In the 1930’s, and to date, however, the majority of First Day Covers have cachets applied to them.