The Basics

Copper - is the metal used. While 2 pieces #5 and #9 have been reported in Brass, neither have been sighted to confirm this.
Size - Diameter 21-22mm. Weight 2-4gms. Die axis of 180º ( inverted), except #6 and #16A at 0º (upright).
Struck - without a retaining collar.

Hard evidence is meagre, and much of that is circumstantial.

When were they made? -
After 1820 is the most likely date, based upon the Coronation medalet of George IV bearing the date July 19, 1821. The reverse of this medalet was muled with an obverse of the Columbia farthing.

Where were they used? -
Generally these pieces are unknown in South America, rare in North America, and common in England.

Where were they made? -
Based on where they were used, England would be the place of origin.

How were they used? -
Evasion or unofficial farthings is probable. While gaming tokens/card counters is a popular theory, the counters were made of brass or gilded to resemble gold. The Columbia farthings are made of copper.

Who made them? -

Can you help to confirm, deny or add to any of the above.