This Data Release contains stream temperature observations for 28 sites in the Antietam Creek Watershed (Maryland) during summer 2021. Data were collected using Onset ProV2 temperature gages within perforated PVC cases attached to stream substrates with rebar. Temperature gages were deployed and retrieved by volunteers with the Antietam-Conococheague Watershed Alliance. Temperature records are provided for 20-minute increments between June 1 and August 31, 2021 (92 days, 6625 observations per site, and a total of 185,500 observations in the dataset). Site location coordinates are provided.