Field measurements of flow velocity were acquired from a reach of the Illinois River at Marseilles, IL, on June 7, 2022, to support research on estimating surface flow velocities from remotely sensed data via particle image velocimetry (PIV). The velocity measurements included in this data release were obtained using a TRDI RiverPro acoustic Doppler current profiler (ADCP) deployed from a boat with an outboard motor. This data release provides depth-averaged flow velocities derived from the raw ADCP data using the TRDI WinRiver II processing software. The spatial location of each velocity measurement was obtained using a differential GPS included as part of the RiverPro instrument package. The map projection and datum for these data are UTM Zone 16 N and WGS84, respectively. This data release consists raw ADCP measurements of flow velocity, channel geometry, and river discharge, provided as raw .mmt and .pd0 files; output from Velocity Mapping Toolbox (VMT) for each ADCP cross-section provided as .xlsx files; and spatial coordinates and depth-averaged flow velocity magnitude and direction for each ADCP cross-section provided as a .csv file. This field-based data set was used to assess the accuracy of remotely sensed estimates of surface flow velocity derived from thermal image sequences via PIV.