The Geostationary Lightning Mapper (GLM) is the first optical lightning detector in geostationary orbit, and GLM sensors operate aboard the National Oceanic and Atmospheric Administration (NOAA) Geostationary Operational Environmental Satellites (GOES R-series: GOES-16, -17, -18, and -19). The first to launch was GOES-16 on November 19, 2016 and it was placed in the GOES-East position. On March 1, 2018 GOES-17 launched and would eventually become operational in the GOES-West position. Since that time, the United States has maintained one satellite in each position. Currently, GOES-18 (west) and GOES-19 (east) are the operational satellites. With these instruments, the combined monthly thunder hour dataset has been created. A thunder hour is an hour during which thunder can be heard at a given location. Thunder hours represent a historical measure of lightning occurrence and a metric of thunderstorm frequency that is comparatively less sensitive to geographic variations in the detection capabilities of a lightning location system. The GLM thunder hour dataset will provide a long-term means of tracking trends in lightning occurrence over the Americas and surrounding oceans. The GLM Combined Monthly Thunder Hour dataset is calculated from lightning detections from 1 January 2019 onward, during which time GLMs are operating from GOES-West and GOES-East positions, providing continuous lightning detection for a broad region from the Aleutian Islands and New Zealand eastward to the western tip of Africa. The data are provided at 0.05° latitude/longitude resolution in netCDF-4 format.