The 18 vehicles were parked relatively close to one another and most were located just a few blocks from the University. Six cars were broken into on Hawthorne Avenue, five on Jefferson Road, five on Westcott Road, one on Hunter Road and one on Linden Lane.
An unlocked bicycle was also stolen from a garage in the same area.
Borough Police Captain Nick Sutter said in an email that there have been no new thefts since Sunday. No arrests have been made so far, but the investigation remains open.
This is not the first time cars have been entered en masse in Princeton. On April 23 of last year, thieves broke into 35 unlocked vehicles on a single Saturday night in Princeton Township in an area also north of the University.
The Borough police are reminding residents to lock their vehicles and bicycles when parked or unoccupied. Any person with relevant information should contact the Princeton Borough Police Department Detective Bureau at (609) 924-4141.