Heat elderberries, cinnamon stick, and water in a saucepan over medium heat. Bring to a boil, reduce heat to low, and simmer for 30 minutes. Use a potato masher to mash berries to release juice.
Strain the juice through a sieve or cheese cloth into mason jars. Let juice cool.
Stir in honey until thoroughly combined. Cover and store in the refrigerator 2 to 3 months.