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​​​​“Child psychiatry is a very fulfilling practice because you can see kids become happy.”​​
Marshfield - Marshfield Medical Center

1000 N Oak Ave
Marshfield, WI 54449

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Provider Bio down arrow

​​Mary Hennessy, M.D., is a child and adolescent psychiatrist at Marshfield Clinic Marshfield Center. She typically sees patients ranging in age from 3 to 21.

​​“The most common complaint we hear about is aggression or disruptive behavior. This occurs at school and at home,” she said. With younger children, she often uses a sand table which children can play in so she can observe their behavior firsthand. Less aggressive children will pretend to feed the toy animals in the sandbox, while the most aggressive will pretend to have the animals eating each other.

“The child’s behaviors mean something and we have to figure out what that is,” she explained. “When you can help a child, you help a lot of people in the process, especially when the parents are really struggling.”​​

Dr. Hennessy earned her medical degree at Georgetown University Medical School in Washington, D.C. She completed her psychiatry residency and a fellowship in child and adolescent psychiatry from the Institute of Living in Hartford, Connecticut, and is board certified in both general psychiatry and child psychiatry.​​

Coming to Marshfield Clinic was an easy decision for her because her husband, Michael McManus, M.D., was already practicing here as a pediatric oncologist/hematologist. They have two grown sons.​​

Professional Summary down arrow

  • Medical School
    Georgetown University - School of Medicine Washington, DC, United States, M.D. 1983

    The Institute of Living Hartford, CT, United States, Psychiatry 1987

    The Institute of Living Hartford, CT, United States, Psychiatry - Child & Adolescent 1988

  • Professional Societies
    American Academy of Child & Adolescent Psychiatry American Psychiatric Association

    Board Certifications
    Child & Adolescent Psychiatry: 1989 Psychiatry: 1988

    State Licenses
    Minnesota Wisconsin

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