Under current U.S. wetland delineation procedures, an area must have hydric soils, wetland hydrology, and hydrophytic vegetation to be considered a wetland. This study investigated the level of correlation between these three parameters on sites disturbed by humans versus relatively undisturbed sites. Based on our data set of nearly 1,800 data points from 188 sites in northeastern Illinois and northwestern Indiana, USA, relatively “disturbed” locations are significantly less likely to meet all three wetland criteria than “undisturbed” locations. Disturbance also affects an area's likelihood to meet or fail particular wetland parameters, depending on the type of disturbance. Also, areas dominated by common hydrophytic species are significantly less likely to meet all three wetland criteria in disturbed areas versus undisturbed areas. This study suggests the need for quantitative studies of the three wetland criteria on both disturbed and undisturbed sites to refine further the USFWS wetness ratings and hydric soil field indicators relative to the effects of disturbance.