I have been told these are "Red Oaks", but the Missouri Department of Conservation lists about 4 species of Oak commonly called Red Oak, and none are a clear match to this one. I live in Southeast Missouri.

I don't know anything about oaks in your end of the country but I do know that the people who will know (about your oak) will want a photo of a leaf (flat with something for measure reference) and an acorn.

Is this Oak in someone's yard? Out in the forest?

@Daisyl My "yard" is the forest. There's an incredible variety of native plants, due to being a riparian habitat. Most of my oaks are "White Oaks". They don't get the bright red leaves. The one in the photo has no acorns yet. The leaves are severely bug eaten. Maybe I can find a (mostly) intact one to measure and photograph.
Thanks for the tips.

Anything grown from a seed can be a cross of two related species. You may not get a definitive identification.

@porkpal
That's a thought. Hybrids happen!

Its pretty though.