[9] The Hillside High School Comets[2] compete in the Union County Interscholastic Athletic Conference, which is comprised of public and private high schools in Union County and was established following a reorganization of sports leagues in Northern New Jersey undertaken by the New Jersey State Interscholastic Athletic Association (NJSIAA).

[19] The 2019 team won its third consecutive Central Jersey Group II title with a 14-10 victory against West Deptford High School in the championship game and went on to finish the season with a 12-0 record.

[20][21] The boys' basketball team won the Group II state championships in both 1990 and 1992, defeating Middle Township High School in the tournament final in both years.

[22] The 1990 team won the Group II state title with a 50-48 victory against Middle Township in the championship game played at the Rutgers Athletic Center[23] and advanced to the Tournament of Champions as the sixth seed, falling to number-three McCorristin Catholic High School by a score 76-49 in the quarterfinals to finish the season with a record of 27-3.

[24][25] The 1992 team won the Group II title in overtime by a score of 62-60 against Middle Township in the championship game played at Rutgers University.

[26] In 2011, the Hillside High School cheerleading team won the title of State Champions at the NJCDCA competition in Trenton in the Intermediate Varsity division.