Current estimates of the magnitude and frequency of floods at gaged and ungaged stream sites are critical for assessing flood risk, delineating flood zones, designing hydraulic structures, and managing flood plains. The Connecticut Department of Transportation collaborated with U.S. Geological Survey (USGS) in a study to improve the flood-frequency estimates in Connecticut and develop regional regression equations for estimating annual exceedance probability discharges at ungaged sites in Connecticut. The results of the study are found in Scientific Investigations Report (http://doi.org/10.3133/sir20205054). This companion data release consists of data compiled and used for the flood-frequency analysis of annual peak flows and development of regional regression equations for Connecticut. The data release is composed of four tables that include: 1) descriptions and locations of streamgages for flood frequency analysis of annual peak flows; 2) updated flood discharges for 152 streamgages for the 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEP) using annual peak data through water year 2015; 3) representation of peak flow data using perception thresholds and interval data in the flood frequency analysis to describe uncertainty and represent missing and historical records; and 4) basin and climatic characteristics that were included as explanatory variables in the regression equations.