Heat sugar and 1 cup water in a small pot until sugar dissolves. Add 1 cup bing cherries, bring to a boil and boil until the cherries begin to soften, about 2-3 minutes. Set aside to cool.
Strain cooled bing cherry syrup into a large pitcher, pressing on the cherries to release their juice. Add lemon juice and cold water. Stir in remaining cherries. Pour over ice and garnish with fresh mint.
Makes 2 quarts