Black knot is so common on cherry, it's an identification characteristic.
I've seen small ornamentals that were covered in Black Knot so much, that the knots outweighed the tree, really, quite interesting. I have also seen many trees with a handful of knots that don't seem to have any effect on the tree, good or bad.
Coming from a small apartment, where everything has to be in order, and every square inch is important, it might be hard to readjust your thinking just a bit now that you are a country person. Rather than cut the tree down, perhaps learning to appreciate the interest, and even beauty, of the tree, complete with it's imperfections.
If the knots are on main limbs or the trunk, you'll want to get a good look and make sure you don't have a safety problem, otherwise, enjoy the character and uniqueness of the growth.