To make the simple syrup, add the cup of water and sugar to a saucepan. Heat and bring to a boil, stirring occasionally, until the sugar has fully dissolved. Remove from the heat and set aside to cool.

Add the 4 cups of cold water, fresh lime juice, and simple syrup to a large pitcher. Stir well to combine and refrigerate until ready to use.

Add 2 cups of the limeade, frozen cherries, and ice to a blender. Blend until the mixture is smooth and slushy. Serve immediately.