A model of plasma transport in the open magnetic field region of the dayside magnetosphere has been used to investigate the source regions and the distribution of solar wind plasma in the magnetospheric cusp and mantle. This model includes the variation in the magnetosheath properties as the plasma accelerates away from the subsolar point, the variation in the transport of magnetosheath plasma across the magnetopause as the orientation of the magnetic field line evolves following reconnection, and the transport of the magnetosheath plasma within the magnetosphere. Our model results are compared with low-altitude spacecraft data from a crossing of the cusp and mantle. We find qualitative and quantitative agreement between the model results and the data. This agreement suggests that the zeroth-order processes included in the model are sufficient to reproduce the commonly observed particle distributions in the low-altitude cusp and mantle regions. ¿ American Geophysical Union 1993