The event happened on Sept. 25 at the Miller Place Inn in Miller Place.
Officials say the number of guests exceeded the state maximum of 50, noting not all attendees were wearing masks.
"We have not seen an event like this before at any time in this pandemic," Suffolk County Executive Steve Bellone said. "For Suffolk County, this was a super-spreader event. This is the first time the health department has taken enforcement action against a business. There was not widespread compliance with face coverings and social distancing as well."
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Bellone said 37 positive cases were connected to that party, nine adults and 28 students, including some from several area high schools. 81 guests (49 students, 32 adults) were quarantined.
"As a result of this one event, 270 people were placed on quarantine," he said. "Eight schools have positive cases and 35 schools had individuals placed under quarantine."
Sachem North High School has been shut down since October 2 because of 15 confirmed cases at the school.
Bellone said Suffolk County began to receive reports of positive cases from the Sachem school district on Sept. 30.
"There is no community spread at this time," he said. "This cluster should serve as a stark reminder of the potential consequences of violating COVID-19 regulations."
There are no known hospitalizations from this event.
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