A recent EPA report on our nation's water quality found that 64% of lakes and 45% of rivers and streams are impaired, water quality has worsened over the last 12 years, and agriculture is a key limiting factor in improving water quality. Poor water quality contributes to diminished productivity, increased treatment costs, damaged global ecosystems, and increased health risks to humans. Further, poor water quality threatens the security of food supplies worldwide. To address agriculture's significant effect on our waterways, reliable water quality models are needed to forecast the water quality consequences of different agricultural nutrient management scenarios. One important agricultural management technology is tile drainage. Tile drainage and drainage management are significant factors determining water quality by expediting nutrient delivery. In this study, the Soil and Water Assessment Tool (SWAT), version 2009, will be applied to simulate stream-flows, riverine nitrate (NO3) export, and watershed nitrogen (N) budgets in the Salt Fork watershed in east-central Illinois, which has extensive corn-soybean cultivation, large N fertilizer input, and extensive tile drainage. The simulation will be calibrated for observed water quality and flow volume data from stream monitoring locations within the watershed. The extent of tile-drainage in the watershed will be based on existing tile maps and inference from land slope and soil hydraulic conductivity. In addition, drainage-related best management practices will be simulated. The calibrated SWAT will predict changes in flow and nitrate export. Lessons learnt from this application of SWAT could lead to more reliable predictions of the water quality outcomes of nutrient management practices in tile-drained watersheds.