In order to ensure that library materials are returned, San Mateo County Libraries will charge patrons replacement fees when an item checked out for 3 weeks has been overdue for 30 days, or when an item checked out for 1 week has been overdue for 7 days. Once an item is returned to the library, the replacement fee will be removed from the patron’s account. The Library may block accounts with excessive charges until items are returned or the charges are paid down.