When the English took possession of the region, the silent "d" was dropped, but was retained in the word "Michigander" because it was pronounced in the French word "Michigandeur".
When the English took possession of this region in 1760 after the French and Indian War, the silent "d" was dropped in the spelling. The "d" in the word "Michigander" was retained, because it was pronounced in the French word "Michigandeur".