FRion computes and applies corrections for the effects of Faraday rotation by the Earth's ionosphere in radio polarization data. In contrast to codes that compute the predicted Faraday rotation measure as a function of time and direction, and in some cases apply the correction directly to visibilities, FRion works where direct correction in visibilities is not possible and correction must occur post-imaging. The package 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. The code uses RMextract (ascl:1806.024) to derive time-dependent Faraday rotation calculations. FRion further applies the correction to Stokes Q and U cubes to remove the effects of the ionosphere.