Medication, antibiotics, and immunization are three major and cost-effective medical interventions but their use is balanced. Knowledge, attitudes and practices (KAP) are a cornerstone. This retrospective study aims at analyzing KAP related to these concerns among the public service population in order to establish the basis for the implementation of selective preventive actions. From a cross-sectional anonymous online questionnaire-based survey among the insurees of a French mutual organization (Union Prévention Santé pour la Fonction publique, UROPS), 33 questions related to medication, antibiotics and vaccination were extracted to evaluate KAP. New variables were constituted: levels of knowledge, antibiotic misuse, proactive behavior and vaccinophobia. Multiple correspondence analysis was performed to identify respondents’ homogenous groups. In addition, bivariate statistical comparisons were provided and logistic regressions were carried out to identify determinants of these new variables. Public service population (workers and retired) were highly exposed to polymedication (8.7% vs. 24.4%, p < 0.0001), hypnotics overtake (24.3% vs. 18.4%, p < 0.0001), and misuse antibiotics (33.2% vs. 22.6%, p < 0.0001) despite good levels of knowledge. Proportions of vaccinophobia was low (0.8% vs. 1.7%, p < 0.0001). However, workers have different KAP than retired, without shared determinants in the 3 health domains studied. Respondents were proactive (85.8% vs. 81.6%, p < 0.0001), used multiple sources of trustworthy information and seems to be ready for the delegation of health tasks. Thus, preventive actions related to antibiotics and polymedication should be a priority in vaccination education for mutual organizations such as UROPS. Studying their insurees longitudinally could be interesting to highlight the impact of selective prevention on behaviors, through trusted health professionals (general practitioners, pharmacists…).