This dataset documents results from 1,041 groundwater samples collected during 1986‒2015 from 16 geologic units in Pennsylvania associated with 25 or more groundwater samples with activities or concentrations of radon-222. Radon-222 is hereafter referred to as “radon.” These 16 geologic units were evaluated in an effort to identify variations in radon concentrations and to classify potential radon exposure from groundwater and indoor air. This dataset was developed for the Pennsylvania Environmental Public Health Tracking (PAEPHT) Program to describe the spatial distribution of radon concentrations in groundwater in Pennsylvania and to illustrate data gaps that exist throughout the State. The PAEPHT Program is part of the National Environmental Public Health Tracking Program funded by the Centers for Disease Control and Prevention (CDC) to improve public health by providing science-based information about the presence of and trends in environmentally related diseases. A focus area for the PAEPHT Program is that of understanding the occurrence of radon concentrations in groundwater and indoor air across the State. This dataset representing radon concentrations in groundwater and describing potential radon exposure from groundwater and indoor air according to geologic units may be used for resource decision-making and risk assessment. This dataset is available from the U.S. Geological Survey (USGS) at https://doi.org/10.5066/F7PR7T74. The companion publication describing the study is at https://pubs.er.usgs.gov/publication/sir20175018 [https://doi.org/10.3133/sir20175018] and is intended to be available through the online databases of the CDC and the PAEPHT programs [http://doh.pa.gov/epht].