Designing a grounding system for a greenfield substation comes with certain difficulties. To start, the only physical item at the location is soil in the ground. Beyond soil resistivity testing, what is an approach for gathering test data on the greenfield substation without the substation existing? The transmission lines and distribution lines that will terminate in the substation may already exist and can be tested to gather information about the existing infrastructure. What will the greenfield substation see for a system grounding impedance during the grounding system analysis? What are or will be the existing metallic paths for fault current to return to the source? Testing the existing infrastructure can provide vital information that can be used during the grounding system design. Additionally, adjacent facilities such as local substations may also be able to provide additional information to the design engineer. Understanding the different soil conditions and how the transmission and distribution lines will interact differently between two substations may allow for an equivalent model to be created that simply shifts the existing substation to the new location. Without testing existing infrastructure in the location where the greenfield substation is going to be installed, the only datapoint that a design engineer might start with is a soil model. If there are multiple soil models created for that location, but there were no other tests completed to existing lines and substations, how will there be certainty that the soil models are accurate or which soil model is the proper model to use for the grounding analysis. This paper will discuss the different methods to approach a greenfield substation design by gathering multiple sets of data from existing facilities, modeling the existing facilities and determining a starting point that leads the design engineer to be confident that the performance of a grounding system will match the estimated model. This paper will then discuss real-world data from case studies where local facilities were tested, with the resulting data used to design the greenfield substation.