Map of German-descent American Genes
You can see very clearly in this map of U.S. counties and their percentage of German blood that North Dakota, South Dakota, Minnesota, and Wisconsin have huge German-descended populations. And you can see that this population concentration radiates outward from these core states to states like Iowa, Nebraska, and Michigan.
My own German family names trace their origins through Wisconsin, Minnesota, and Nebraska. And I'm writing this post from North Dakota, where 50% of the ancestry here is German. Another 30% here in North Dakota is Norwegian, which is Sigrid, my wife's ancestry.
Map of German-American population percentages in the United States
States in America with the largest German-descent White Populations