FRion computes and applies corrections for the effects of Faraday rotation by the Earth's ionosphere in radio polarization data. Other ionospheric Faraday rotation codes can compute the predicted Faraday rotation measure as a function of time and direction, and in some cases apply the correction directly to visibilities. FRion has been made to tackle the case where direct correction in visibilities is not possible and correction must occur post-imaging. FRion computes the time-averaged Faraday rotation across the duration of an observation, which should serve as a reasonable approximation for the effect of the ionosphere in radio interferometer images. For the ionosphere Faraday rotation calculations we use the external package RMextract (ascl:1806.024). FRion can further apply the correction to Stokes Q and U cubes to remove the effects of the ionosphere.