<p>Previous studies found that individuals with mental illness may have cognitive distortions. However, their findings are far from conclusive since most research focused on depression while less attention was paid to other mental illnesses such as anxiety and suicidal ideation. In addition, differences in cognitive distortions across individuals with different mental illnesses such as anxiety, depression, and suicidal ideation remain underexplored. To address these issues, this study investigated 12 types of cognitive distortions in individuals with symptoms of anxiety, depression, and suicidal ideation based on an analysis of their language use patterns on social media. The analysis yielded several findings of interest. First, individuals with symptoms of anxiety, depression, and suicidal ideation showed significantly higher cognitive distortions than those without mental illness. More specifically, they were characterised by significantly higher cognitive distortions of dichotomous reasoning, labelling and mislabelling, overgeneralizing, and personalizing. Second, individuals with symptoms of anxiety, depression, and suicidal ideation differ from one another in cognitive distortions. Individuals with more severe symptoms of mental illness have higher cognitive distortions such as dichotomous reasoning. These findings have significant clinical implications for the diagnosis of and prevention of mental illness.</p>