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We present a study of the diffuse ionized gas (DIG) in three Sculptor groupgalaxies: NGC 55, NGC 253, and NGC 300. The study is based on narrow bandimagery in H-alpha+[NII](6548+6583A) and [SII] (6717+6731A). We find that DIGcontributes 33 to 58% of the total H-alpha luminosity in these galaxies, or 30to 54% after correcting for scattered light. We find that NGC 300 has a higherfractional DIG luminosity than the other galaxies in our sample, but it is notclear whether this is a significant difference or an effect of the highinclination of the other galaxies. The diffuse emission, averaged over theoptical extent of the disk, has a face-on emission measure of 5 to 10 pccm^{-6}. The DIG is concentrated near HII regions, although significantemission is seen at large distances from HII regions, up to 0.5 to 1 kpc. The[SII]/(H-alpha+[NII]) ratio is enhanced in the DIG, typically around 0.3 to0.5, compared to 0.2 for the HII regions in these galaxies. These propertiesare similar to those measured for the DIG in the Milky Way and in other nearbyspirals. The line ratios, large-scale distribution, and energy requirementsuggest that photoionization is the dominant ionization mechanism.Comment: 19 pages, LaTex, 3 LaTex tables, 4 Postscript figures, 3 jpeg plates.  Plates also available at ftp://astro.nmsu.edu/pub/choopes/ , accepted for  publication in the Astronomical Journal. Replaced version includes plate

Diffuse Ionized Gas in Three Sculptor Group Galaxies