Ion implantation at plasma-facing surfaces is affected by the formation of the electrostatic sheath potential. The average energy of an ion can increase by more than a factor of three as a result of the sheath and the effect on ion implantation can be significant. In this paper, Monte Carlo calculations of plasma ion implantation are carried out including the effect of the sheath. The calculations incorporate a simulation of the velocity distribution of plasma ions incident on a surface with a floating potential. The effect of the surface floating potential is included in a new analytic model for plasma implantation. The new model should provide a fast and accurate means to calculate the distribution of plasma ion implantation.