This dataset includes four tables related to annual trends in streamflow metrics at 599 reference streamgages in the conterminous United States for the period 1955-2014. Reference streamgages are defined here as gages with drainage basins that are minimally impacted by anthropogenic effects such as reservoirs or urbanization. The four tables are: 1) computed annual values for 16 streamflow metrics, 2) trend estimates for the 16 streamflow metrics for the period 1955-2014, 3) metric names and definitions, and 4) location information (latitude and longitude) for the 599 sites. The computed annual values for the 16 streamflow metrics are: low flow magnitude, low flow frequency, low flow duration, high flow magnitude, high flow frequency, high flow duration, skew, daily rises, Spring low flow percentage, Spring high flow percentage, Summer low flow percentage, Summer high flow percentage, Fall low flow percentage, Fall high flow percentage, Winter low flow percentage, and Winter high flow percentage. The annual flow metrics were estimated by Eng and others (2017) from daily streamflow records at the 599 reference streamgages. Sen slope trend values and confidence intervals for the 16 flow metrics for the period 1955-2014 were computed from the annual time series using the non-parametric Theil-Sen approach (Sen, P., 1968). In addition to the Sen slope, the median value for each metric for the period 1955-2014, the percentage change in each metric over the period 1955-2014, and a percentage change class for each metric also are reported.