How to counter Jayce
Let us take a look on how to beat Jayce. We will look at champions who are strong against Jayce and who are weak against Jayce. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Jayce. You can already win in champion select with the right counters for Jayce. If you want to know how to counter Jayce then you need to take into account the best picks vs Jayce and the worst picks vs Jayce. This Jayce 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 Jayce or whether they played as Jayce.
Champions used by Pros to counter pick Jayce
Looking at the matches from Pros (see table Pros counter picked Jayce) we can see that they picked 
Twisted Fate most often to counter pick Jayce. The matchup Twisted Fate vs Jayce occured 50 times. Jayce has 30 wins and 20 losses in this matchup. Learn how to counter pick Twisted Fate to get another perspective on the data.
Lane outcome for Jayce
When looking at Jayce 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 Jayce. The lane outcome of Jayce consists of three outcomes: Win, Loss or Draw. Let's take a look of Jayce 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 Jayce.
Conclusion
Analyze the available data and learn how to beat Jayce. To master Jayce take also a look on Jayce builds and runes for Jayce. Good luck, Summoner!