Until recently, there has been a scarcity of comprehensive, consistent, timely, and geospatially-detailed information about irrigation needed to support studies linking agricultural land use change to processes like contaminant transport or aquifer water use. MODIS data are being used to refine mapping of irrigation patterns across the country. Peak annual NDVI values for 2012 are computed from MODIS data that represent a proxy for maximum vegetation vigor. These peak NDVI values are applied in models in conjunction with Agricultural Census and NLCD data to capture irrigated patches and patterns across the agricultural landscape.The development of an irrigated lands dataset representing the 2012 time period completes a decadal series (2002, 2007, 2012) of national geospatial data that can be used to help assess and evaluate water-quality trends in ground and surface waters. The 2012 dataset also provides an opportunity to evaluate irrigated lands in current SPARROW models as an explicit vector for nutrient and sediment transport. Finally, the increased spatial details of the irrigated lands dataset allow refinement of current water volumes used for agricultural irrigation.