If canning, prepare a water bath canner for a hot pack before starting. Also, prepare pint jars and rings.
Bring all ingredients (except tomatoes) to a boil in a 6-quart stockpot or dutch oven. Simmer 10 minutes, stirring frequently.
Add the tomatoes to the pot and cook an additional 5 minutes. (Be sure not to add the tomatoes at the beginning, they'll fall apart into sauce.)
Ladle the corn relish into prepared canning jars, leaving 1/2 inch headspace. Debubble jars, wipe rims and apply 2 part canning lids to finger tight.
If canning, use a jar lifter to load the jars into a water bath canner and process pint jars for 15 minutes (if below 1,000 feet in elevation, see altitude adjustments in notes for higher elevations). Turn off the heat and let the jars stand for an additional 5 minutes in the canner before removing them to cool on a towel on the counter.
After 24 hours, check seals and store any unsealed jars in the refrigerator for immediate use. Properly canned and sealed jars can be stored in the pantry shelf and will keep 12-18 months.