Despite increased awareness of concussions among student-athletes, local epidemiologic surveillance efforts are limited, especially among adolescents. We analyzed data reported through a state public-school-based online surveillance tool during the fall (summer preseason and regular season), winter, and spring seasons of the 2015–2017 school years at seven participating public high schools across New Jersey. Concussions were sustained during interscholastic and intramural sports and in physical education classes. There were 208 concussions: 142 in fall (123 regular season), 22 in winter (21 regular season), and 44 in spring. Reports stated 75% were first concussions, but 17% were second and 2% were third concussions.