Dillingham was born and raised in Hickory, North Carolina. He emerged as one of the top high school basketball players at Combine Academy during his sophomore season. During his sophomore year he averaged 21.2 points per game. He joined Overtime Elite during his senior season and averaged 14.7 points per game.
He was ranked as the #13 overall prospect by 247Sports. He was named the Iverson Classic Crossover Award winner for his performance in the 2023 Iverson Classic.
Dillingham signed with the Kentucky Wildcats over several other offers. In his freshman year at Kentucky he is averaging 15.4 points per game entering the 2024 NCAA tournament.