This article explores the environmental and market determinants of irrigation management in a five-state Great Lakes region. We found evidence that corn, soybean, and potato irrigators respond to the cost of water at the intensive margin. Evidence of a water-cost effect at the extensive margin was mixed. This article is unique in its geographic focus and its consideration of various temperature effects. We found evidence of a long-run average temperature effect on crop acreage allocation decisions and a short-run extreme heat effect on water application rates.