How to counter Ornn
Let us take a look on how to beat Ornn. We will look at champions who are strong against Ornn and who are weak against Ornn. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Ornn. You can already win in champion select with the right counters for Ornn. If you want to know how to counter Ornn then you need to take into account the best picks vs Ornn and the worst picks vs Ornn. This Ornn counter data is based on matches played by Pros on patch 15.12 and previous ones. It is important to see whether Pros counter picked Ornn or whether they played as Ornn.
Champions used by Pros to counter pick Ornn
Looking at the matches from Pros (see table Pros counter picked Ornn) we can see that they picked 
Rumble most often to counter pick Ornn. The matchup Rumble vs Ornn occured 15 times. Ornn has 8 wins and 7 losses in this matchup. Learn how to counter pick Rumble to get another perspective on the data.
Lane outcome for Ornn
When looking at Ornn counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Ornn. The lane outcome of Ornn consists of three outcomes: Win, Loss or Draw. Let's take a look of Ornn lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Ornn.
Conclusion
Analyze the available data and learn how to beat Ornn. To master Ornn take also a look on Ornn builds and runes for Ornn. Good luck, Summoner!