I am in Illinois. The last 3 weeks have been very bad for fungal infections. The combination of high humidity and quite a bit of rain hasn’t been good.
Looking at the pictures you supplied you may have cherry leaf spot. Picture two looks like cherry leaf spot. Picture three looks like something else. But it would take more pictures of the leaves with some of the leaves in earlier stages of infection to be more accurate in a diagnosis.
I would take a look at this thread dealing with cherry leaf spot and the links included in it.
Here is another thread you might find useful.
I usually spray my cherries with Daconil or Captan mixed with Immunox to control leaf spot. Which has worked in the past. Currently, I use Captan mixed with Indar.
I usually have a few leaves drop in high heat periods in the Summer. It’s a small portion of the leaves and not a problem. The leaves don’t have any spots on them when the heat alone is the cause of the dropping.