Ooh, spicy question. Polenta is also ground corn. But it’s usually from a different variety. Polenta uses flint corn, which is harder and more yellow.
Grits are typically from softer white corn. But honestly? In a blindfold test, you might not tell the difference. It’s more about tradition and texture.
Polenta is often cooked stiff and sliced. Grits are usually served soft and spoonable. But you do you. I won’t call the grits police.