 From 1973-77, Grotberg served two terms in the Illinois House of Representatives, and in 1976, he easily won an election to the Illinois Senate where he served three terms as Illinois State Senator (1977–85), the last four years of which he was the Assistant Republican Leader.As a ranking Republican in the Illinois legislature, he won election to Congress in November, 1984 for an open seat in a heavily Republican district, and was a member of the Banking, Finance, and Urban Affairs and Small Business Committees.Two bills which carried his mark were an amendment to the Defense Department authorization urging the armed forces to "use domestic equipment when entertaining in federal buildings" (prompted by an observation of a Yamaha piano being used by the Navy Choir at the Capitol)  and Public Law 99-202, the Save for the USA Year, which resulted in "the largest number of savings bonds sales in the United States in several decades."