Mid-American Energy built a total of 50 huge turbines, which produce about 75,000 KW of electricity. The wind farm was constructed in early 2008.
We also saw an even larger windfarm on I-35, near the Minnesota/Iowa border. I think it is called "Top of Iowa" (there are maybe three different "sites" within the same area). Started almost 10 years ago (built in 2001), it contains a total of 147 turbines.