A Mount Pleasant man is in custody for sexual assault involving a child. The Mount Pleasant Police Department arrested 19-year-old Joseph Erdman following an investigation prompted by a report on June 4th. According to the police department, the assault involved a 5-year-old. Erdman is charged with 2nd degree sexual abuse, a class B felony. The investigation is ongoing. Anyone with information related to this case can contact the police department at 319-385-1450.