Students who spoke with ABC7 Eyewitness News said the video, which circulated on Snapchat, showed a male and female student engaged in a sex act in the presence of three other male students inside one of the school's bathrooms.
Police confirm everyone involved is a juvenile and do not expect any charges to be filed.
Evanston Township High School issued a one-sentence statement on the incident: "Whenever there is a claim of this nature, the district investigates thoroughly, and maintains the privacy and confidentiality of student information."