The largest source of positioning error for single-frequency users of the Global Navigation Satellite System (GNSS) is typically the radio delay caused by the ionosphere. Although several analytic function-based models for correcting ionospheric errors are available, grid-based models are preferred because of their high estimation accuracy and low complexity. We propose an adaptive ionospheric pierce point cut-off radius control algorithm for the high-resolution, grid-based correction of ionospheric errors. The proposed scheme adjusts the IPP cut-off radii by comparing the target IPP densities with the current effective densities. Simulation results show that our method gives the required effective IPP density using this cut-off radius control, thus improving the accuracy and availability of the correction service. It is expected that the proposed scheme will make high-resolution, grid-based ionospheric correction available for Korean satellite navigation systems with a local distribution of ground reference stations. System development costs will also be reduced since it will require fewer reference stations.