Whiskey production began in the U.S. in 1773 when the British
government passed the Molasses Act which made mollasses from the
French colonies not economical to use. Until that time, the colonists
produced spirits from imported molasses.
1) George Washington's mash bill (c.1797)
corn 30%, rye 65%, malt 5%
2) Rye whiskey (typical)
corn 39%, rye 51%, malt10%
3) Bourbon (typical)
corn 70%, rye 15%, malt 15%
4) Tennnessee whiskey (typical)
corn 80%, rye 10%, malt 10%
So you can see early American whiskey was actually a rye whiskey. The
German settlers who first made it called it Kornbrand or Korn. The
mash bill for Dutch genever (gin) was originally 2/3 rye, 1/3 malt.
These days it is 1/3 maize, 1/3 rye, 1/3 malt. The British use of the
word corn refers to grains in general. I gather 'corn' (maize) was
originally called 'Indian corn'.
As a comparison, the mash bill for Scottish grain whisky (and London
Dry Gin!) is -
corn 75%, wheat 10%, malt 15%