Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.