We investigated the frequency of brain fog in a large cohort of patients with documented coronavirus disease-2019 (COVID-19) who have survived the illness. We also scrutinized the potential risk factors associated with the development of brain fog. Adult patients (18-55 years of age), who were referred to the healthcare facilities anywhere in Fars province from February 19, 2020 to November 20, 2020 were included. All patients had a confirmed COVID-19 diagnosis. In a phone call, at least 3 months after their discharge from the hospital, we obtained their current information. A questionnaire was specifically designed for data collection. In total, 2696 patients had the inclusion criteria; 1680 (62.3%) people reported long COVID syndrome (LCS). LCS-associated brain fog was reported by 194 (7.2%) patients. Female sex (odds ratio [OR]: 1.4), respiratory problems at the onset (OR: 1.9), and intensive care unit (ICU) admission (OR: 1.7) were significantly associated with reporting chronic post-COVID "brain fog" by the patients. In this large population-based study, we report that chronic post-COVID "brain fog" has significant associations with sex (female), respiratory symptoms at the onset, and the severity of the illness (ICU admission).