Judge Mike Grigsby is a life-long resident of Union County. Since 1981 he has maintained a private law practice here. From 1981 to 1985 he served on Marysville City Council as Councilman-at-large, and was President of Council in 1982, 1983 and 1984. Judge Grigsby was Marysville's Law Director and Municipal Court Prosecutor from January 1, 1986 to December 31, 1999. He belongs to the Ohio, and Union County Bar Associations and is admitted to practice before the United States, Ohio and Minnesota Supreme Courts, and the U.S. District Courts for the Northern and Southern Districts of Ohio and the District of Minnesota.

In November 1999, he was elected Judge of Marysville Municipal Court. He is also a Trustee of the Union County Board of the American Red Cross and the Union County Community Improvement Corporation, a division of the Chamber of Commerce, and served as alternate member of the Logan-Union-Champaign Planning Commission.

He is an associate member of the Union County Township Clerks and Trustees Association, Union County Farm Bureau, past Secretary of the Marysville Evening Lions, Trustee of the Union County Law Library, and belongs to several lodges and fraternal organizations.