Digital flood-inundation maps for a 9.9-mile reach of Dardenne Creek, St. Charles County, Missouri, were created by the U.S. Geological Survey (USGS) in cooperation with St. Charles County, Missouri Department of Transportation, and the cities of O'Fallon and St. Peters, Missouri. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Program at http://water.usgs.gov/osw/flood_inundation/, depict estimates of the areal extent and depth of flooding corresponding to select water levels (stages) at the USGS streamgages 05514860 Dardenne Creek at Old Town St. Peters, Missouri, and 05587450 Mississippi River at Grafton, Illinois. Near-real-time stages at these streamgages may be obtained from the USGS National Water Information System database at https://doi.org/10.5066/F7P55KJN or the National Weather Service Advanced Hydrologic Prediction Service at https://water.weather.gov/ahps2/hydrograph.php?wfo=lsx&gage=drcm7 (USGS streamgage 05514860) and https://water.weather.gov/ahps2/hydrograph.php?wfo=lsx&gage=grfi2 (USGS streamgage 05587450), which also forecasts flood hydrographs at these sites. Flood profiles were computed for the Dardenne Creek stream reach by means of a one-dimensional model for simulation of water-surface profiles with steady-state flow computations. The model was calibrated using the current stage-discharge relation at the USGS streamgages 05514840 Dardenne Creek at O'Fallon, Missouri, and 05514860 Dardenne Creek at St. Peters, Missouri, and documented high-water marks from the flood of December 2015. The hydraulic model was then used to compute 16 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from 16 ft (near bankfull) to 32 ft, at the USGS streamgage 05514860 Dardenne Creek at Old Town St. Peters, Missouri. Files that correspond to this layer can be found in the child items section named Flood Inundation Shapefile for Dardenne Creek, St. Charles County, Missouri, 2019. and Flood Inundation Depth Grids for Dardenne Creek, St. Charles County, Missouri, 2019. Stages in the lower Dardenne Creek can be influenced by backwater from the Mississippi River, therefore, 23 sets of water-surface profiles ranging from 18 ft to 40 ft were developed and referenced to USGS streamgage 05587450 Mississippi River at Grafton, Illinois. Files that correspond to this layer can be found in the child items section named Flood-Inundation Depth Grids for Dardenne Creek Backwater, St. Charles County, Missouri. 2019. and Flood-Inundation Shapefile for Dardenne Creek Backwater, St. Charles County, Missouri. 2019. The upper stage for each map library exceeds the stage corresponding to the estimated 0.2-percent annual exceedance probability flood (500-year recurrence interval flood) at the streamgage locations. The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging (lidar) data having a 0.26-ft vertical accuracy and 0.71-ft horizontal resolution) to delineate the area flooded at each water level. The availability of these maps, along with information regarding current stage from the USGS streamgages and forecasted high-flow stages from the National Weather Service, will provide emergency management personnel and residents with information that is critical for flood mitigation, preparedness and planning, flood-response activities such as evacuations and road closures, as well as for post-flood recovery efforts.