Multiple thermal protection techniques, including thermal barrier coatings (TBCs), internal cooling and external cooling, are employed for gas turbine components to reduce metal temperatures and extend component life. Understanding the interaction of these cooling methods, in particular, provides valuable information for the design stage. The current study builds upon a conjugate heat transfer model of a blade endwall to examine the impact of a TBC on the cooling performance. The experimental data with and without TBC are compared to results from conjugate computational fluid dynamics (CFD) simulations. The cases considered include internal impingement jet cooling and film cooling at different blowing ratios with and without a TBC. Experimental and computational results indicate the TBC has a profound effect, reducing scaled wall temperatures for all cases. The TBC effect is shown to be more significant than the effect of increasing blowing ratio. The computational results, which agree fairly well to the experimental results, are used to explain why the improvement with TBC increases with blowing ratio. Additionally, the computational results reveal significant temperature gradients within the endwall, and information on the flow behavior within the impingement channel.