Used (aka cancelled) 19th century US stamps are highly collectible, just like unused 19th century US stamps. In addition to the rarity and condition of the stamp itself, collectors also focus on the quality and rarity of the cancellation (also known as the 'cancel,' or 'killer').

Many 19th century US stamps were hand-cancelled by local postmasters, to prevent re-use of the stamp. Handmade cancels were often carved from cork in a wide variety of creative designs, sometimes referred to as fancy cancels.

Lightly cancelled stamps, with the postmark on a small corner of the stamp, are typically more valuable than heavily-cancelled ones. One exception is the so-called 'bulls-eye' cancellation, where an entire postmark is readable on the stamp, allowing collectors to see the time, date, and location where the stamp was used.