Abstract This field guide focuses on key outcrops that highlight recent nomenclatorial changes of Early Silurian strata in western Ohio (e.g., Dayton Formation, Osgood Formation, Laurel Formation, Lewisburg Formation, Massie Formation, Euphemia Dolomite), as well as the Brassfield Formation and Springfield Dolomite. The field trip begins near the apex of the Cincinnati/Findlay Arch at a quarry in Ludlow Falls, Ohio, and ends at a more offshore position to the southeast, near Clifton, Ohio. Recent conodont biostratigraphic and δ 13 C carb chemostratigraphic data for many of those formations at the field trip localities clearly demonstrate coeval stratigraphic patterns present throughout western Ohio that were previously obscured due to prior inconsistent lithostratigraphic terminology and correlation. Those data also help to show important differences in stratigraphic patterns in western Ohio. Strata correlative to the Lee Creek Formation are recognized for the first time near the apex of the Cincinnati/Findlay Arch in western Ohio in West Milton, Ohio, and are tentatively identified as that formation. At the same locality the Dayton is shown to be completely absent, and the Osgood Formation overlies a thin unit tentatively identified as the Lee Creek Formation and underlying Brassfield Formation. The Springfield Dolomite at the Barrett Paving Materials Ludlow Quarry in Ludlow Falls, Ohio, contains trilobites of the Gravicalymene celebra Association, one of the most taxonomi-cally diverse and geographically widespread trilobite associations in the Silurian of North America. Pentamerid brachiopods occur with molts of Gravicalymene celebra in the Springfield there, suggesting an environmental complexity not seen elsewhere; pentamerids are not found in strata containing the Gravicalymene celebra Association in most other areas of the Midwest.