The long-term effects on the mental health of people living with COVID-19 are emerging as a global threat to public health. This study aimed to determine the levels and risk factors associated with depression, anxiety and stress (DAS) among COVID-19 infected adults discharged from a hospital in a high-risk area in Thailand. A cross-sectional study was performed with 512 participants aged 18 years and above who had been infected with COVID-19 and discharged between 3 and 12 months in Hat Yai District, Songkhla Province, Thailand during March, 2022. A structured questionnaire was used to collect the data based on the short version of the Depression, Anxiety, and Stress Scale – 21 Items (DASS-21) with a content validity index of 0.89 and Cronbach’s alpha coefficient of 0.86. Demographic information, medical history, and the present health status of each participant were also collected. Almost all the respondents had severe depression (62.7%), extremely severe anxiety (82.6%), and moderate and severe stress (45.3% and 41.0%, respectively). There was a positive correlation between depression and stress among COVID-19 survivors (R = 0.155, p < 0.001). Factors associated with depression were a medical history of pulmonary disease (β = 1.443, p = 0.042) and higher education status (β = 1.067, p < 0.001), whereas lower body mass index (BMI) (β = 0.455, p < 0.001) and lower monthly income (β = 1.067, p < 0.001) were associated with stress. Participants who were tested for COVID-19 for travel, study, job, and examination application (all β > 0.575, all p = 0.001), and lower BMI (all β > 0.601, all p < 0.011) were also associated with anxiety. The findings of our study could provide baseline information for follow-up intervention initiatives to prevent long-term effects of COVID-19.