A geo-fencing system stores a geo-fence associated with a geographic location of a user equipment device (UE). The geo-fencing system receives, from a Network Exposure Function (NEF) or Service Capability Exposure Function (SCEF) in a mobile network, a monitoring event (MONTE) location report associated with a current location of the UE within the mobile network, and extracts a Radio Access Network (RAN) location from the MONTE location report, where the RAN location identifies a cell, cell sector, eNodeB (eNB), gNodeB (gNB), or tracking area (TA) associated with the current location of the UE. The geo-fencing system determines, based on a comparison of the identified cell, cell sector, eNB, gNB, or TA with the stored geo-fence, whether the UE has entered or exited the geo-fence, and sends, based on the determination, a geo-fence alert to the NEF or SCEF for forwarding to a geo-fencing enabled application.