Dennhardt (February 5, 1869 – March 19, 1929) was an American auctioneer, businessman, and politician.
Born in Naumberg, Saxony in what is now Germany, Dennhardt emigrated to the United States and settled in Wisconsin as a young man.
He was in the implement business and was an auctioneer.
Dennhardt served in the Wisconsin State Assembly in 1911 and was a Republican.
He then served in the Wisconsin State Senate in 1919.
In 1922, Dennhardt served as mayor of Neenah, Wisconsin.