In a 6- to 8-quart heavy pot combine sugar; crushed strawberries, blueberries, and raspberries; lemon peel; and lemon juice. Bring to boiling over medium heat, stirring to dissolve sugar. Boil gently, uncovered, for 25 to 30 minutes or until mixture sheets off a metal spoon, stirring frequently. Whisk in cinnamon until thoroughly combined.
Ladle hot jam into hot sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
Process filled jars in a boiling-water canner for 10 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks. Makes 10 half-pints.