Serna joined the U.S. Soccer Development Academy with the Rapids' academy in 2009. After graduating from high school, he played one year of college soccer for the University of Akron and signed with the Rapids as a homegrown player in January 2013. Dillon also trained with the full U.S. National squad in January of 2015, along with teammate Shane O’Neill. Named to the squad for the 2011 CONCACAF U-17 Championship and the 2011 FIFA U-17 World Cup in Mexico. In July 2012, he joined the U.S. U-20 National Team for the Milk Cup in Northern Ireland, playing in all three of the team’s matches. Was called up to the January U-20 training camp and added to the roster for the CONCACAF U-20 Championship where he played in three matches and the U.S. qualified for the 2013 FIFA U-20 World Cup.