During water years 2016–2021 (a water year begins on October 1 and ends on September 30 and is designated by the year in which it ends), the U.S. Geological Survey (USGS), in cooperation with the Illinois Environmental Protection Agency (Illinois EPA), operated continuous monitoring stations on eight of the major rivers in Illinois to better quantify nutrient and sediment loadings from the State of Illinois to the Mississippi River. These eight rivers are the Illinois River, Rock River, Little Wabash River, Kaskaskia River, Vermilion River, Embarras River, Big Muddy River, and Green River. This data release presents estimates of daily nitrate, phosphorus, and suspended sediment concentrations and uncertainty over that period. The concentration estimates are based on a combination of discrete sampling and surrogate regression (imputation); see Hodson and others (2021) for details on the imputation model. The data release comprises a single comma-separated values (csv) file containing daily timeseries of concentration and uncertainty for each monitoring station. These data supersede Hodson and others (2021b), which was based on data through water year 2020. Reference cited: Hodson, T.O., Terrio, P.J., Peake, C.S., and Fazio, D.J., 2021a, Continuous Monitoring and Bayesian Estimation of Nutrient and Sediment Loads from Illinois Watersheds, for water years 2016–2020: U.S. Geological Survey Scientific Investigations Report 2021-5092, https://doi.org/3133/sir20215092. Hodson, T.O., Terrio, P.J., Peake, C.S., and Fazio, D.J., 2021b, Modeled nutrient and sediment concentrations from major rivers in Illinois based on continuous monitoring from October 1, 2015, through September 30, 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9MS8OIH.