In a 6- to 8-quart heavy pot combine sugar, peaches, whiskey and lemon juice.
Bring to boiling over medium heat, stirring to dissolve sugar.
Quickly stir in pectin.
Bring to a full rolling boil, stirring constantly.
Boil hard for 1 minute, stirring constantly.
Remove from heat and quickly skim off foam with a metal spoon.

Ladle hot jam into hot sterilized half-pint canning jars, leaving 1/4-inch headspace.
Wipe jar rims; adjust lids and screw bands.

Process filled jars in a boiling-water canner for 5 minutes (start timing when water returns to boiling).
Remove jars form canner; cool on wire racks, turning and tilting jars after 20 minutes to distribute fruit evenly throughout the jam.
Repeat as necessary.
Makes 7 half-pints.