Add the cherries, lemon juice, and sugar to a large saucepan over medium heat. Bring to a boil. Reduce the heat and let simmer for about 3 minutes.
In a cup, mix the cornstarch with the water to remove any lumps. Add the cornstarch mixture to the pot and stir. Reduce the heat to low an continue simmering for 5-7 minutes or until the cherries have released their juices and softened and the sauce has thickened.
Remove the pot from the heat and let cool to room temperature before storing or using.
Notes
Storage and Freezing:Homemade cherry pie filling will last for about 5 days in the fridge, in an airtight container. A glass jar with a lid is perfect.Or once completely cooled you can freeze the cherry filling for up to 4 months. Let thaw in the fridge before using.Depending on how you want to use it, you may want to reheat it gently on the stovetop so that it regains the glossy texture.