Planning policy for parks is typically guided by a standard approach that fails to account for how communities actually use parks. Moreover, few researchers know the exact parks people use, even though “use” is often hypothesised in the relationships being tested. Public participatory geographic information systems (PPGISs) present an opportunity to collect specific, spatially referenced information on park use and park-based activities. However, the reliability of these instruments has not been studied. The Park Life PPGIS captured residential location, park location, and park-based behavioural data from a sample of adults and was tested for reliability. Kappa scores and intra-class correlations assessed the reliability of the items. Recall of individual items all showed acceptable reliability and mostly achieved “substantial” agreement or “near-perfect” agreement. The Park Life PPGIS is a reliable instrument to capture park use and activities. Such information is essential for public health and physical activity researchers, urban planners, and park managers to develop informed planning and public health policies and programs that promote park use.