Objective: To investigate the impact of coronavirus disease 2019 lockdown on glycemic control and associated factors in people living with type 1 diabetes. Research design and methods: An observational evaluation from a self-reported questionnaire on behavioral changes and glycemic information from flash glucose monitoring (FGM) during the lockdown in 1,378 individuals living with type 1 diabetes who used a French dedicated nationwide web application (CoviDIAB). Results: The main outcome was the change of the mean glucose level 2 months before and 1 month after the lockdown. We found that mean glucose improved from 9.1 ± 1.7 mmol/L to 8.7 ± 1.7 mmol/L (P < 0.001). Factors associated with better glycemic control were a decrease of alcohol consumption (odds ratio [OR] 1.75 [95% CI 1.04-2.94]), an increase in the frequency of FGM scans (OR 1.48 [1.04-2.10]) and in the number of hypoglycemia events (OR 1.67 [1.13-2.46]), and an easier diabetes control perception (OR 1.71 [1.18-2.49]). Conclusions: Our findings suggest that lockdown has a positive impact on glycemic control in people with type 1 diabetes.