How to counter Riven
Let us take a look on how to beat Riven. We will look at champions who are strong against Riven and who are weak against Riven. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Riven. You can already win in champion select with the right counters for Riven. If you want to know how to counter Riven then you need to take into account the best picks vs Riven and the worst picks vs Riven. This Riven counter data is based on matches played by Pros on patch 14.20 and previous ones. It is important to see whether Pros counter picked Riven or whether they played as Riven.
Champions used by Pros to counter pick Riven
Looking at the matches from Pros (see table Pros counter picked Riven) we can see that they picked 
Renekton most often to counter pick Riven. The matchup Renekton vs Riven occured 22 times. Riven has 10 wins and 12 losses in this matchup. Learn how to counter pick Renekton to get another perspective on the data.
Lane outcome for Riven
When looking at Riven 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 Riven. The lane outcome of Riven consists of three outcomes: Win, Loss or Draw. Let's take a look of Riven 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 Riven.
Conclusion
Analyze the available data and learn how to beat Riven. To master Riven take also a look on Riven builds and runes for Riven. Good luck, Summoner!