A floodplain sedimentation model quantifies sediment budgets for U.S. mid-Atlantic Piedmont river corridors. Regional regression equations estimate discharge events every 3 months, and (temporally invariant) channel width and slope. River stage is assessed using steady uniform flow equations, corrected for nearby mill dams. Sediment concentrations are computed with a rating curve (defined for modern conditions by gaging station data). Spatially uniform floodplain deposition occurs during overbank flows, while stored sediment is eroded based on age. Calibration to modern (1950-2017) floodplain sediment thicknesses determines the effective sedimentation velocity, which is equivalent to the settling rate of fine silt. Tuning the model to floodplain stratigraphic data suggests that presettlement (before 1750) suspended sediment concentrations were 5-8% of those prevailing today, while legacy (1750-1950) sediment concentrations were 25-35% of present values. Because the available stratigraphic data are not correlated with maximum deposit age, the time of initial deposition is selected randomly by the model, creating variable outcomes for any single set of model parameters, resulting in an incomplete calibration of the model for presettlement conditions. Nonetheless, the model accurately reproduces the observed age distribution of floodplain deposits. All sediment budgets components computed using the model increase monotonically from presettlement time to the present, and the ratio of budget components remains similar from one time period to the next. The model also predicts that millennial timescales are needed for mid-Atlantic floodplains to equilibrate following a change in sediment regime, a finding with important implications for river corridor and watershed restoration planning.