How to counter Sion
Let us take a look on how to beat Sion. We will look at champions who are strong against Sion and who are weak against Sion. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Sion. You can already win in champion select with the right counters for Sion. If you want to know how to counter Sion then you need to take into account the best picks vs Sion and the worst picks vs Sion. This Sion counter data is based on matches played by Pros on patch 14.12 and previous ones. It is important to see whether Pros counter picked Sion or whether they played as Sion.
Champions used by Pros to counter pick Sion
Looking at the matches from Pros (see table Pros counter picked Sion) we can see that they picked 
Rumble most often to counter pick Sion. The matchup Rumble vs Sion occured 8 times. Sion has 6 wins and 2 losses in this matchup. Learn how to counter pick Rumble to get another perspective on the data.
Lane outcome for Sion
When looking at Sion 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 Sion. The lane outcome of Sion consists of three outcomes: Win, Loss or Draw. Let's take a look of Sion 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 Sion.
Conclusion
Analyze the available data and learn how to beat Sion. To master Sion take also a look on Sion builds and runes for Sion. Good luck, Summoner!