We examined bat activity levels, species composition, and collision mortality at a large wind plant in southwest Minnesota from 15 June-15 September, 2001 and 2002. We found 151 bat casualties, most of which were hoary bats (Lasiurus cinereus). We recorded 3,718 bat passes at bat foraging and roosting areas within 3.6 km of the wind plant (x̄ = 48/detector-night) and 452 bat passes at wind turbines (x̄ = 1.9/detector-night). Peak bat activity at turbines followed the same trend as bat mortality and occurred from mid-July through the end of August. Based on the timing of fall bat migration, we believe that most bat mortality involved migrating bats. There was no significant relationship between bat activity at turbines or the number of fatalities and presence of lights on turbines. We captured 103 bats comprised of 5 species in mist nets. Big brown bats (Eptesicus fuscus) comprised most of the captures. Our study indicated that there were relatively large breeding populations of bats near the wind plant when collision mortality was low to nonexistent. Future research should concentrate on determining causes of bat collisions and methods to reduce or mitigate the mortality.