The U.S. Geological Survey (USGS) works closely with the Mississippi Department of Transportation (MDOT) to provide information to be used by the MDOT for design of highway-drainage structures. MDOT spends millions of dollars annually for highway construction. Streamflow records, hydrologic analyses of basins, and hydraulic analyses of flooding potential at proposed highway crossings help the MDOT to make more informed decisions on the use of highway construction funding. Flood-frequency and hydraulic characteristics at highway crossings are determined from historical flood-elevation data recovered by the USGS, cross-section data, and correlations with data from nearby gaging stations. Additional streamflow data are collected for ungaged sites when substantial flooding occurs in an area of interest to MDOT. This information not only provides the basis for the design of highways and drainage structures, but is also used by local agencies and the public as a guide in flood-plain management. Data for twenty-one sites in Mississippi that were studied during the State fiscal year 2024 (July 1, 2023 to June 30, 2024) are provided in this data release. The geospatial dataset includes one point feature class shapefile with associated FGDC-compliant metadata representing selected basin characteristics and estimates of eight flood-frequency peak streamflows with corresponding stages, or water-surface elevations for twenty-one sites in Mississippi. Flood-frequency streamflows were determined using methods described by Anderson (2018, 2021). Water-surface elevations were determined using methods described by Rantz (1982a, 1982b). Also included are input files of the step-backwater model described by Shearman (1990). Anderson, B.T., 2018, Flood frequency of rural streams in Mississippi, 2013: U.S. Geological Survey Scientific Investigations Report 2018–5148, 12 p., [Also available at https://doi.org/10.3133/sir20185148]. Anderson, B.T., 2021, Magnitude and frequency of floods in the alluvial plain of the lower Mississippi River, 2017: U.S. Geological Survey Scientific Investigations Report 2021-5046, 15 p., https://doi.org/10.3133/sir20215046. Rantz, S.E., and others, 1982a, Measurement and Computation of Streamflow--vol.1, Measurement of Stage and Discharge: U.S. Geological Survey Water-Supply Paper 2175, p. 1-284, [Also available at https://doi.org/10.3133/wsp2175]. Rantz, S.E., and others, 1982b, Measurement and Computation of Streamflow--vol.2, Computation of Discharge: U.S. Geological Survey Water-Supply Paper 2175, p. 285-631, [Also available at: https://doi.org/10.3133/wsp2175]. Shearman, J.O., 1990, User’s manual for WSPRO—A computer model for water-surface profile computations: U.S. Department of Transportation Publication No. FHWA–IP–89–027, Hydraulic Computer Programs HY–7, 177 p. [Also available at: https://water.usgs.gov/software/WSPRO/].