Select a baking sheet that will fit on one of your freezer shelves, then line it with parchment paper.
Arrange the watermelon chunks into a single layer on the lined baking sheet, making sure that the pieces aren't touching, so they won't stick together later. Place the pan in the freezer, and allow them to freeze for 2-4 hours.
Once the watermelon is frozen, transfer the pieces to an airtight container, so they won't pick up any other flavors from your freezer. Frozen watermelon can be stored in the freezer for 3 to 6 months when it's tightly sealed.
You can freeze as much or as little watermelon as you'd like to, so the amount listed here is only a suggestion. For a watermelon "ice pop" try sticking a popsicle stick into one of the fresh watermelon cubes. When you freeze it, it will turn into a cute, mini-size frozen treat.