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Abstract The lack of iron‐reducing capability in some red soils poses an issue for determining the suitability for on‐site wastewater treatment systems (OSWWTS). The Arkansas Department of Health allows for placement of OSWWTS in certain red‐clay soils that have the potential for iron reduction and do not show expansiveness upon wetting, but only in the Ozark Highlands (Major Land Resource Area [MLRA] 116A), which is referred to as the red‐soil exception. The objectives of this study were (a) to confirm the nonexpansiveness and iron reducibility of select soils in the Ozark Highlands that meet the criteria for the red‐soil exception, and (b) to compare the expansiveness and iron reducibility of the residual or colluvial red‐clay soils of the Ozark Highlands with those in four other MLRA region groupings in Arkansas. Fresh and archived soils were used to create a 51‐sample dataset from the 38‐ to 50‐cm soil depth interval for analyses. The alluvial soils of the Red and Arkansas River valleys had a mean coefficient of linear extensibility (COLE) of 0.116 mm mm–1, whereas the residual or colluvial soils from the other MLRA regions evaluated had lower (P < .01) COLE values. Soils from the Red and Arkansas Rivers region changed red color (∆A) the least (∆A of −8.6 in the LAB color scheme; P < .01) compared with soils from the other regions. Results of this study indicate that the red‐soil exception, as used by the Arkansas Department of Health for determining OSWWTS suitability, could be expanded to include soils from several additional MLRAs with additional, site‐specific information.