This data release contains estimates of annual nitrate, suspended sediment, phosphorus, and chloride loads and uncertainty from sites in the Illinois Environmental Protection Agency (Illinois EPA) Ambient Water Quality Monitoring Network. The loads were estimated using Weighted Regressions on Time, Discharge, and Season with Kalman filtering (WRTDS-K) and existing discrete water-quality data and discharge data collected by Illinois EPA, the U.S. Geological Survey, and Illinois State Water Survey through water year (WY) 2020. All water-quality and discharge data used in this work are available from the Water Quality Portal and the National Water Information System. The data release comprises a single comma-separated values (CSV) file containing annual loads, load uncertainty, and sample counts for each Ambient monitoring station.