The deal includes $9.53 million of fully guaranteed money and can be worth up to $18.25 million.
Cohen's extension comes as the Bears reportedly continue negotiations with wide receiver Allen Robinson.
Chicago selected Cohen in the fourth round of the 2017 NFL Draft. He's amassed 250 carries for over 1,000 yards in three seasons and also provides value to the Bears' inconsistent passing game.
Cohen rushed for 41 yards on seven carries in the Bears' Week 1 win over the Detroit Lions.