The phrase William and Mary usually refers to the co-regency over the Kingdoms of England, Scotland and Ireland, of spouses and first-cousins King William III & II and Queen Mary II. Their joint reign began in February 1689. They replaced James II & VII, Mary's father and William's uncle and father-in-law.
The pattern farthings with William on one side and Mary on the other were struck as experimental pieces and never entered circulation. There is no date on the coin. Several other patterns, some with William and some with Mary, were also produced. Circulating coins show both William and Mary on one side.
These are generally rare pieces. The price goes up substantially with condition: the better the condition, the higher the price. They were struck in both silver and copper. Here are some approximate catalog values:
worn: $50 US dollars approximate catalog value
average circulated: $100
well preserved: $300
worn: $90 US dollars approximate catalog value
average circulated: $180
well preserved: $400
Use our Important Terminology page to convert these catalog values to actual buy and sell values.