Little is known about the epidemiological characteristics of patients with coronavirus disease 2019 (COVID-19) in Japan. This is a retrospective observational study of COVID-19 patients; study was conducted from February 1 to May 31, 2020. We used publicly collected data on cases of COVID-19 confirmed by polymerase chain reaction (PCR) testing in Osaka Prefecture, Japan. We described the patient characteristics. The Cox proportional-hazards model was applied to evaluate the association between factors (sex, onset month, age group, city of residence) and mortality, and hazard ratios (HRs) with 95% confidence intervals were estimated. During the study period, 5.7% (1782/31,152) of individuals who underwent PCR testing for COVID-19 showed positive results. Among 244 patients with information on symptoms, the most common symptom was fever (76.6%), followed by cough (44.3%). Of the 1782 patients, 86 patients died. Compared with those aged 0–59 years, higher mortality was observed among those aged 60–69 years (HR: 12.02 [3.37–42.93]), 70–79 years (HR: 44.62 [15.16–131.30]), 80–89 years (HR: 68.38 [22.93–203.89]), and ≥90 years (HR: 144.71 [42.55–492.15]). In conclusion, in Osaka Prefecture, Japan, the most common symptom was fever, and older adults had higher mortality among COVID-19 patients.