How to counter Evelynn
Let us take a look on how to beat Evelynn. We will look at champions who are strong against Evelynn and who are weak against Evelynn. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Jungle champion who counters Evelynn. You can already win in champion select with the right counters for Evelynn. If you want to know how to counter Evelynn then you need to take into account the best picks vs Evelynn and the worst picks vs Evelynn. This Evelynn counter data is based on matches played by Pros on patch 15.4 and previous ones. It is important to see whether Pros counter picked Evelynn or whether they played as Evelynn.
Champions used by Pros to counter pick Evelynn
Looking at the matches from Pros (see table Pros counter picked Evelynn) we can see that they picked 
Lee Sin most often to counter pick Evelynn. The matchup Lee Sin vs Evelynn occured 10 times. Evelynn has 4 wins and 6 losses in this matchup. Learn how to counter pick Lee Sin to get another perspective on the data.
Lane outcome for Evelynn
When looking at Evelynn 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 Evelynn. The lane outcome of Evelynn consists of three outcomes: Win, Loss or Draw. Let's take a look of Evelynn 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 Evelynn.
Conclusion
Analyze the available data and learn how to beat Evelynn. To master Evelynn take also a look on Evelynn builds and runes for Evelynn. Good luck, Summoner!