Indian River Lagoon (IRL) is one of the most biologically diverse estuarine systems in the continental United States, stretching 200 kilometers (km) along the Atlantic coast of central Florida. The width of the lagoon varies between 0.5–9.0 km and is characterized by shallow, brackish waters with significant human development along both shores. Scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center, working in collaboration with the St. Johns River Water Management District, collected time-series of surface water radon-222 (radon-in-water) during two sampling periods in 2017 to investigate submarine groundwater discharge at Indian River Lagoon (IRL). Time-series radon data were collected at two sites, Eau Gallie North and Riverwalk Park, along the western shore of IRL. Eau Gallie North (EGN) is near the central section of IRL while Riverwalk Park (RWP) is approximately 20 km north of the Eau Gallie site. Stationary instrument moorings were deployed concurrently with continuous radon surface water mapping along shore-parallel transects conducted by the U.S. Geological Survey in May, September and November surveys outlined in previously published data releases (https://doi.org/10.5066/F7QF8S05 and https://doi.org/10.5066/F76Q1WG4). At each of the two study sites, a nearshore mooring (~10 meters (m) from shore) and an offshore mooring (~80-120 m from shore) were deployed to collect time-series of surface water radon-222 for six days. Surface water was continuously pumped into an air-water exchanger, where dissolved radon-222 was purged from the water into a gaseous phase inside the exchanger. Radon-222 in the exchanger was continuously pumped into and measured by a commercially available radon-in-air detector (RAD7, Durridge, Inc). Water temperatures in the exchanger, as well as water level and conductivity, were measured every 5 minutes. Radon-in-air measurements were corrected to radon-in-water activities using the temperature-salinity dependent air-water partitioning coefficient (Schubert and others, 2012). This data release contains the radon-222 time-series data, water temperature, conductivity, salinity and water level data collected during the mooring deployments of the May 2017, September 2017, and November 2017 surveys.