Who was the inventor of the windmill?

No one knows who exactly invented the very first wind-powered mechanism. It is believed that the first wind-driven mills were produced in the Middle East and quickly spread to Europe.

If you mean the first American farm windmill, the inventor was Daniel Halladay in 1854, whose company, the U.S. Wind Engine and Pump Company, was later moved to Batavia, Illinois, where it became one of the most successful windmill companies in the country.