Students and staff were told to immediately begin a period of self-quarantine through March 27, Mayor Judah Zeigler said in a letter to the community.
All Leonia Middle School students who attend the SACC program, and all SACC staff who work at the Anna Scott school, were asked to do the same.
"This means that you should remain in your homes, and monitor yourself for any symptoms," the mayor said. "If you are feeling unwell, you should contact your physician."
Zeigler even went so far as urging residents who want to check on their neighbors to do so by calling, texting or emailing them and not visiting.
Borough officials also banned dining in at borough restaurants -- allowing takeout and delivery only -- while closing all Leonia parks, Borough Hall, the recreation center and the public library to the public.
Bergen County Executive Jim Tedesco warned earlier Sunday that the entire county could soon go on virtual lockdown.
Leonia's school district buildings will remain closed at least through April 13, following the week-long spring break, Zeigler said.
"As a result of the latest developments, the distribution of computers from the Leonia School District will be delayed until Monday afternoon (March 16), or Tuesday morning (March 17)," the mayor said. "Details will be communicated directly from the superintendent of schools.
"For families that participate in the Leonia School District lunch program, the pickup location has been changed to the front entrance of Leonia Middle School (pickup will NOT be available at Anna C. Scott school)," Zeigler added. "For families that chose home delivery, the process will remain unchanged.
"All borough restaurants have been directed to offer takeout or delivery service only; no dine-in service is permitted at any borough food establishment until further notice.
"All borough parks are closed and off-limits to everyone until further notice," the mayor said.
Borough staff will be available by telephone and email, he said.
Visit www.leonianj.gov for an employee directory as well as available online services.
All non-essential borough board and commission meetings are indefinitely postponed.
All borough residents are "strongly encouraged to limit their interaction with non-family members not living with you, as well as others, and limit any unnecessary local and other travel," Zeigler said. "This includes visits to other borough residents unless necessary.
"If you would like to check on your neighbors, please do this via telephone, email or text."
Click here for updates from across New Jersey.
Click here to follow Daily Voice Cresskill-Closter and receive free news updates.