- 3 cups water
- 3 cups white sugar
- 4 cups fresh mint leaves, packed - divided
- 3 (1.5 liter) bottles Kentucky whiskey
- 5 pounds ice cubes, or as needed
- 6 cups ice water, or as needed
- Bring 3 cups water to a boil in a saucepan and stir in sugar until dissolved. Bring to a boil, reduce heat to medium, and boil the syrup until it becomes clear, about 2 minutes. Remove from heat.
- Stir 1 cup mint leaves into the simple syrup and allow to cool thoroughly. Pour syrup and mint leaves into a container with a lid. Mix in 1 more cup mint leaves, cover, and refrigerate mint syrup at least 4 hours or overnight.
- Pour whiskey and chilled mint syrup into a large cooler or drink dispenser.
- To serve, fill 10-ounce glasses with ice and dispense 2 to 4 ounces mint julep mixture into each glass. Top with ice water and 1 or 2 mint leaves per cocktail and stir.