Research finds mentally ill persons have higher rates of police contacts, arrests, and criminal charges for minor offenses and noncriminal behavior. It remains unclear whether the decision-making process and factors affecting discretion reflect a procedural bias that criminalizes the mentally ill. Using observational data from a Canadian police service, the findings suggest higher odds for criminal charges with serious offenses, males, older citizens, a prior criminal record, being under the influence of alcohol or drugs, and being uncooperative with requests for information and compliance. The odds of a citation are higher for proactive calls, more serious offenses, older citizens, mentally ill persons, those under the influence, or with a disrespectful demeanor. The overall findings suggest an indirect procedural bias exists due to situational constraints, a disjuncture between policy and police culture, and limited mental health resources that lead to response strategies that contribute to criminalization of the mentally ill.