Following a public health alert raised by general practitioners questioning a possible excess of glioblastoma cases in the municipalities of Salindres and Rousson (Gard) in 2010, two epidemiological studies were conducted from 2006 to 2010, and then from 2011 to 2015, using data from the National Histological Registry of Primary Tumors of the Central Nervous System (RnhTPSNC). The second study confirmed the existence of an excess of cases from 2011 to 2015 and over the broader 2006–2015 period, and recommended refining the environmental investigation into the presence of potential sources of ionizing radiation—a known risk factor for glioblastomas—and continuing the study for another five years. The Institute for Radiation Protection and Nuclear Safety (IRSN) subsequently dispelled any doubts by concluding that there were no radiological anomalies in the area. This report presents an update of the two previous studies covering the entire 2006–2020 period. To this end, two approaches were considered: (i) the first, similar to previous studies, involved investigating the occupational history of the cases from Salindres and Rousson at the industrial site, calculating standardized incidence ratios (SIR) for the area of the two municipalities using the rest of the Gard department as a reference, and conducting a sensitivity analysis of the standardized incidence ratio (SIR) calculations; (ii) the second, a novel approach, involved conducting a spatio-temporal scan analysis using the entire department as the study area. The results of these two approaches confirm an excess incidence of histologically confirmed glioblastomas in the Salindres and Rousson area, with a significant SIR of 3.06 over 2006–2020 (approach 1). More broadly, an excess incidence is confirmed in an area covering a larger sector in the northern part of the Gard department, well beyond the boundaries of the two municipalities alone, as evidenced by the presence of several significant clusters in this sector (approach 2). Furthermore, the study highlights an average annual increase in the incidence of these tumors of 3.2% in the Gard, a trend that is geographically consistent. Given these results and the low plausibility of a very large portion of the population in the northern sector of the Gard being exposed to established risk factors such as ionizing radiation, the lack of strong hypotheses regarding the role of other risk factors that could guide the investigation, and the overall trend toward an increase in the incidence of histologically confirmed glioblastomas in the Gard department, in France, and internationally, it is proposed to place the situation observed in the Gard within a broader framework of improving knowledge of the risk factors for this disease, and of the reasons that could explain the increase in the incidence of glioblastoma cases at various geographic scales (departmental, national, international). Efforts in this direction are thus being made by the international scientific community. This is the case in France, with the establishment in 2023 by the National Cancer Institute and Santé publique France, an expert committee on the rising incidence of glioblastomas, and the ongoing work by the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) on the carcinogenic effects of radiofrequency radiation.