Kennen Counters: A list

• Don't pick a champion with only an engage mobility spell. Nothing is worse than having no mobility and being chased by a 500 MS ball of electricity.
• Ward. If he is in a bush and you facecheck, he can surprise you, stun you, and kill you.
• If he uses his E and your jungler is around, ask them to gank
• His E uses half his energy pool. You have 10 seconds before he gets it all back and he can use his E again.
• If his ult is up, never towerdive or try to engage. Kennen can easily disengage you.
• His ult is only managed by his cooldown. That cooldown is 2 minutes. If you overwelm him, he will have nothing but retreating or death.

I hope this helps you. Or atleast stops the complaining about this champion on the boards even though he isn't OP.