Cut shucked corn cobs in two pieces.
Place in a large stockpot, add enough to cover the cobs.
Bring to a boil.
Reduce heat and simmer 40 minutes.
Strain the corn juice through a double layer of cheesecloth or a jelly bag.
Measure 3 cups of corncob juice into a large pot. (Water may be added if needed to make 3 cups liquid.)
Whisk in the pectin and bring to a boil.
Add the sugar and bring the mixture back to a full roiling boil while stirring.
Boil for 5 minutes.
Remove from heat; skim off foam.
Pour hot jelly immediately into hot, sterile jars, leaving ¼-inch headspace.
Wipe rims of jars with a dampened clean paper towel; adjust two-piece metal canning lids.
Process 5 minutes in a boiling water bath. Adjust for altitude above 1000 ft.
Remove from water bath and cool completely before storing in a cool place.