On 20 December 2015, three THEMIS spacecrafts detected a nightside magnetotail reconnection event at about 04:36 UT. The spacecrafts (P5, P4, and P3) had their footprints located over North America in the near vicinity of the Gillam ground magnetometer station in Canada. Multipoint observations, both in space and from the ground, allow for an examination of the spatiotemporal characteristics of the disturbance on the ground and the associated physical drivers in the magnetosphere and ionosphere. This study shows that the geomagnetic field dB/dt localization observed at Gillam ground magnetometer site was caused by an isolated substorm onset near that location driven by a nightside magnetotail reconnection event detected by three THEMIS spacecrafts that were located near the central plasma sheet. This event represents the first observation of ground dB/dt localization that is directly linked to nightside magnetotail fast flow bursts and reconnection event.