Google has taken an equity stake in the project in Greene County being developed by RPM Access.
The wind farm, near Des Moines, uses Nordex turbines and has a deal to sell its power to utility Central Iowa Power Cooperative.
Google says the investment is part of its commitment to “greening the grid” in Iowa, where it operates a data centre.
It takes Google’s renewables investment to more than $990m, says the company, which has backed major wind and solar ventures around the US over the last few years.