Herro attended Whitnall High School in Greenfield, Wisconsin. In his senior season, he was named to the First Team All-State as he averaged 32. 9 points, 7. 4 rebounds, 3. 6 assists, and 3. 3 steals per game; he also shot better than 50 percent from the floor and 43. 5 percent from behind the three-point line. He tallied in excess of two thousand points over his high school career. He initially committed, albeit verbally, to the University of Wisconsin on September 12, 2016, only to renege about a year later, having a keener interest in playing for the Kentucky Wildcats. Herro committed to the University of Kentucky on November 14, 2017.