The passage of the 1850 Federal Swampland Act facilitated the drainage of thousands of acres of Illinois land, producing some of the most fertile cropland in the world. Some 10 million acres, about 35% of the total agricultural area in the state, are drained. Drainage systems have a significant effect on the hydrology and water quality of the watersheds in which they occur, and there is a strong correlation between improved drainage and elevated nutrient transport from cropped land. In recent years, conservation drainage practices, that is, practices that are optimized for both water quality and production benefits, have been introduced into the State. The Illinois Conservation Drainage Research/Demonstration Program was established to monitor the performance of these practices, and to conduct research on new and innovative ones. In addition, the data from monitored conservation drainage systems are being used to update and calibrate the Illinois Drainage Guide.