Several species of conodonts in the Columbus and Delaware limestones of north-central Ohio are segregated stratigraphically and form associations that correspond fairly well to lithofacies in which they occur. Polygnathus linguiformis , P. angusticostatus , P. angustipennatus , P. intermedius , and Panderodus sp. appear to have been benthic creatures sensitive to substrate texture and energy levels. Other species of Polygnathus may have been benthic, but a nektonic habit is possible for some. Prioniodina tortoides preferred deep-water conditions but was likely nektonic. Simple-cone taxa other than Panderodus and species of Icriodus are ubiquitous and considered to have been shallow-pelagic plankton or nekton. Icriodus orri shows some preference for near-shore environments. Associations similar to some in this area occur in New York, central Ohio, and southwestern Ontario. Endemic forms appear to define a faunal realm limited to the Illinois, Appalachian, and southeastern Michigan basins that is distinct from a realm extending westward and northwestward from the northern to westernmost Michigan Basin. Barriers to intermixing of endemics involved tectonic elements but also hypersalinity and other environmental factors.