I was wondering, what are the max stats in this game?

Like I know you can have 35 tenacity, 40% cool down reduction and 2.5 attack speed.

But what about Ad, Ap, Armor, Magic Resist, Movement speed, etc?

Movement speed has a soft cap of 490. Any amount over it will be halved.

I can't think of any others at the moment.

Capped by items.

For example, you could stack runes, Bloodthirsters, pick someone like Nocturne and Yi with their insane AD steroids, and get close to 800+ AD... And that's the cap.

Tenacity, CDR, and Attack Speed are capped because of how they work - it would be totally possible to get 100% CDR or Tenacity, and if your attack Speed was any higher than 2.5, I'm pretty sure the animations would break.

Of course, MR, movement speed, and armor have softcaps/diminishing returns... So I guess that is close to a cap.

Technically, u can have 75 tenacity (Ireila)

tenacity isn't capped its just that all items that give it are unique and the highest is merc treads giving 35
and im pretty sure that AS and CDr and the only capped stats in the game
tho movement speed gets a soft cap at +415 and a bigger one at +490
thats it tho

Oh, so theres no Impassible amount Attack Damage or Ability Power can reach? They just keep going until you reach the limit of your characters items/abilites//runes?

Yep

CDR is hard capped at 40% as you said. The only other hard cap I'm aware of is 2.5 AS.

Many stats give diminishing returns via multiplicative scaling on percents and can thus never get 100%. These are slows, dodge, and tenacity. Tenacity from items does not stack.

Don't forget about the Dodge cap. I believe it's 40% even though the champion stats you view in-game can show higher.