Ground Truth Data is data that comes from a known source, where the truth about the data is known and not inferred (FSR, 2021). The Forensic Science Regulator requires forensic units (that carry out certain forensic processes) to undertake tests against ground truth data for the purposes of quality assurance/quality control processes such as accreditation. However, the data collected must form a meaningful dataset that will enable relevant tests to be performed that inform the end-user. This technical note discusses how a forensic unit in the UK planned and developed a method for collecting ground truth data for footwear mark evidence. It discusses the materials and variables that were considered when developing the method and the evidence-based, decision-making processes that enabled its creation. Recommendations and considerations are provided to assist other forensic units collect data relevant to their jurisdiction. Whilst the method is not prescriptive, if it is used as a guide, it may facilitate the development of a large and relevant national dataset.