Hello again, MSM --
If your farthing looks like the one in the picture, i.e., a nice coin, it may draw $1 US dollar from a collector who wants to add it to his or her collection. Otherwise, it is worth less. A fully uncirculated specimen -- one that passed from the mint directly into a coin collection -- would probably bring $5.
The farthings dated 1938 and 1939 were struck in smaller numbers (though still in the millions) and as such command a slightly higher value of about $10 when in fully uncirculated condition.
These values apply to all George VI farthings with a wren on the back. Starting in 1949 the 'IND:IMP' disappears from the inscription. After 1952 Queen Elizabeth replaces King George on the front of the coin.
For more that you'll ever want to know about farthings, go to AboutFarthings.com.