Nitrate contamination of drinking water, common in agricultural areas, increases the risk of certain cancers and impacts fetal development during pregnancy. Building on previously published methodology, this study evaluates nitrate-attributable disease cases and adverse birth outcomes as well as their economic costs for Wisconsin, USA. Nitrate is the most common contaminant in groundwater in Wisconsin. Two-thirds of the state’s residents use groundwater as the primary source of drinking water. Here, we analyze nitrate exposure from drinking water in Wisconsin based on nitrate test results for community water systems for the period of 2010-2017 and a novel methodology for estimating nitrate exposure for the 28% of state’s residents who use private wells. We estimate that annually, 111-298 combined cases of colorectal, ovarian, thyroid, bladder, and kidney cancer in Wisconsin may be due to nitrate contamination of drinking water. Each year, up to 137-149 cases of very low birth weight, 72-79 cases of very preterm birth, and two cases of neural tube defects could be due to nitrate exposure from drinking water. The direct medical cost estimates for all nitrate-attributable adverse health outcomes range between $23 and $80 million annually. Simulating targeted reductions in the counties with the highest current drinking water nitrate concentrations resulted in similar reductions in adverse health outcomes as statewide reduction efforts, up to nitrate reductions of 20%. Time trend analysis suggests that groundwater nitrate concentrations are overall increasing. Thus, nitrate contamination of water supplies in Wisconsin is a public health problem that needs to be addressed.