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The stratigraphic interval for this investigation extends from the top of the Middle Devonian Onondaga Limestone to the base of the Upper Devonian Berea Sandstone. Devonian shale source rock geochemistry and thermal maturity data were compiled from all available published sources and from archived data for 201 wells in eastern and central Ohio. From this comprehensive database, maps of total organic carbon (TOC), existing hydrocarbons (S₁), hydrocarbons generated during pyrolysis (S₂), vitrinite reflectance (%R[subscript o]), and conodont alteration index (CAI) were constructed to better refine the source rock generative potential and thermal maturity of the Devonian shale interval in eastern Ohio. Generally, westward increases in TOC, S₁, and S₂ were evident from these preliminary maps. Maximum TOC values per well ranged from 0.5 to 18.4 percent with over 70 percent of the wells having values greater than 4 percent, which is considered excellent source rock potential. The maximum value of TOC for the Devonian shale was over twice that of the Upper Ordovician Utica-Point Pleasant interval in eastern Ohio. The maximum S₁ value was 8.6 milligrams of hydrocarbons per gram (mg HC/g) of rock (excellent source rock generative potential) and generally ranged from 1 to 2 mg HC/g of rock (good source rock generative potential). Maximum S₂ values were often in the range of 10-20 (very good) or 20-40 (excellent) mg HC/g rock. Thermal maturity maps using %R[subscript o] and CAI revealed a basinward (eastward) transition to more thermally mature rocks. Maximum vitrinite reflectance values ranged from 0.33 to 1.34 %R[subscript o]. A 0.6 %R[subscript o] isograd trends northeast-southwest through eastern Ohio, marks the onset of oil generation, and separates the immature region to the west. The oil window transitions eastward to a condensate or wet gas window at values between 1.1 and 1.4 %R[subscript o]. "Vitrinite suppression" was indicated by both a comparison with %R[subscript o] of the overlying coals and with reported historic production. While current Devonian shale horizontal drilling is focused on the Marcellus Shale, these maps and data present strong evidence that other organic-rich Devonian shale units, such as the overlying Huron Shale Member and Rhinestreet Shale Member, also have significant oil and gas potential and may be good candidates for modern-day horizontal drilling techniques.