If using fresh cherries, remove the pits. (You can skip this step by using frozen cherries since they’re already pitted.)
Combine water, sugar, and cherries in a small pot over medium heat.
Bring to a boil, stirring occasionally until the sugar dissolves.
Reduce to low heat and let mixture bubble until it starts to foam, about 5 minutes. Using a potato masher, crush the cherries to release all of their juices.
Remove from heat and allow to cool for 10-15 minutes.
Pour the cooled mixture through a fine mesh strainer set over a bowl. Discard the cherry pieces.
Store your cherry simple syrup in a mason jar or other glass, airtight container in the refrigerator for up to 2 weeks.