How to counter Xerath
Let us take a look on how to beat Xerath. We will look at champions who are strong against Xerath and who are weak against Xerath. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters Xerath. You can already win in champion select with the right counters for Xerath. If you want to know how to counter Xerath then you need to take into account the best picks vs Xerath and the worst picks vs Xerath. This Xerath counter data is based on matches played by Pros on patch 15.13 and previous ones. It is important to see whether Pros counter picked Xerath or whether they played as Xerath.
Champions used by Pros to counter pick Xerath
Looking at the matches from Pros (see table Pros counter picked Xerath) we can see that they picked 
Orianna most often to counter pick Xerath. The matchup Orianna vs Xerath occured 8 times. Xerath has 3 wins and 5 losses in this matchup. Learn how to counter pick Orianna to get another perspective on the data.
Lane outcome for Xerath
When looking at Xerath 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 Xerath. The lane outcome of Xerath consists of three outcomes: Win, Loss or Draw. Let's take a look of Xerath 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 Xerath.
Conclusion
Analyze the available data and learn how to beat Xerath. To master Xerath take also a look on Xerath builds and runes for Xerath. Good luck, Summoner!