A detailed investigation of the St. Peter Sandstone of southwestern Wisconsin was undertaken to describe its sedimentologic texture in modern quantitative terminology, to determine its environment of deposition, and to test the available techniques of environmental analysis. The St. Peter Sandstone of southwestern Wisconsin is a fine, moderately well-sorted, nearly symmetrical, mesokurtic sand. Grain-size frequency distributions tend to exhibit a weakly-developed bimodality. Significant regional and stratigraphic variations were observed in mean and maximum grain size, sorting, and skewness, consistent with changes in local paleotopography and regional paleoslope. Environmental interpretations based on five bivariate grain-size parameter combinations and two linear discriminant functions were judged to be inadequate because of serious flaws inherent in these techniques. A more satisfactory. approach toward predicting the sedimentary environment is achieved with two cumulative probability curve techniques and with the regional and stratigraphic variations in single grain-size parameters. A lower foreshore to shallow marine sand bank environment is deduced.