Corrosion monitoring has been the focus of structural health monitoring due to its damaging effects on metallic structures. Early detection of environmental factors responsible for corrosion can reduce maintenance related expenses. There is growing interest in developing compact and low-cost thin film sensors with high sensitivity to corrosion precursors. In this work, chemical sensors are fabricated using solution processed C60 organic thin film transistors (OTFTs) coated with functionalized graphene oxide for humidity sensing and functionalized graphene nanoparticles for Cl- detection. The fabricated OTFTs exhibit good carrier mobilities and current ON/OFF ratios reaching 1.2 cm2/V.s and 5x103, respectively. The rGO coated OTFT humidity sensor is designed for qualitative measurements, and it exhibits a relative responsivity for dry to surface wetness transition of 122.6%, with a response time of 20 ms. Chemically functionalized hydrogenated graphene coated OTFT is used for Cl- ion sensing which yielded sensitivity of 4%/ppm to ultrafine ionic concentrations.