This dataset is a running trend analysis of baseflow from USGS stream gage records from as early as 1911 to 2016 for 23 unregulated streams across the five largest Hawaiian Islands: Kauai, Oʻahu, Molokaʻi, Maui, and Hawaiʻi. First, we separated mean daily flow into direct run‐off and baseflow with the “lfstat” separation procedure in R, which employs the Institute of Hydrology (1980) standard baseflow separation procedure of 5‐day blocks to identify minimum flow, called a turning point. The turning points are then connected to obtain the baseflow hydrograph. For each stream, Sen's slope and Mann–Kendall statistic were calculated incrementally using the R package “trend” to give window sizes from 10‐107 years depending on length of the flow record. Initial mean daily stream flow data were obtained from the U.S. Geological Survey (https://waterdata.usgs.gov/nwis/rt).