It has been observed that the degree of pulmonary involvement shown in chest computed tomography (CT) scans tended to decrease as the prevalence of coronavirus disease 2019 (COVID-19) infection decreased in the Turkish population. The purpose of this study was to investigate the relationship between the disease severity based on chest CT scans and the temporal evolution of the epidemic. This study recruited 179 patients with confirmed COVID-19 disease who had received a chest CT scan between March 14 and April 28, 2020. The participants were divided into three successive temporal groups based on their date of CT examination. The early (March 14–29), mid (March 30–April 13), and late (April 14–28) groups were compared regarding the presence and extent of pulmonary involvement and CT characteristics of lesions. COVID-19 pneumonia was less extensive in participants under 45 years of age and patients presenting late in the course of epidemic (i.e., the late group) compared those presenting earlier. When each group was subcategorized on the basis of age, older patients in the late group had less extensive lung involvement than older patients in the early group. However, there was no significant difference in the extent of lung involvement in younger patients between the late and early groups. The severity of COVID-19 pneumonia appears to be variable at different temporal windows of the epidemic curve and decreases in patients presenting in the later weeks compared to the earlier weeks, particularly in older patients.