This digital dataset contains historical geochemical and other information for 100 samples of groundwater from 71 wells located within 3 miles of the Poso Creek Oil Field in Kern County, California. An additional 12 wells in the Poso Creek study area, but co-located within 3 miles of the adjacent Rosedale and Rosedale Ranch Oil Fields, were not included in this data release; these data are planned for a future data release associated with those fields. The sampled wells include water-supply wells used primarily for domestic, irrigation, and industrial uses. Numerical water chemistry data were compiled from two data sources: 1) Kern County Public Health Services Department (KCPHSD) PDF (Portable Document Format) files, and 2) the Eastside Water Management Area (EWMA) Groundwater Sustainability Plan (GSP) Chapter. These data sources include varying location and well-construction information. Locations for most of the wells represent either well-specific coordinates provided in the KCPHSD PDFs, approximate locations determined using ArcGIS (GIS, Geographic Information System) software based on descriptive information or location maps in the KCPHSD PDFs, parcel centroid coordinates determined from a GIS parcel shapefile (KERN PARCEL) based on parcel numbers provided by either the KCPHSD or EWMA data source, or approximate locations from Google Earth based on visual identification of well locations. For two wells (Dataset_IDs 1 and 2) coordinates represent the locations provided by the California Department of Water Resources Water Data Library (CDWR WDL) as those particular wells are located in that database in association with water-level measurement data. For three wells (Dataset_IDs 22, 30, and 42) having limited information, locations represent meridian, township, range, section, and quarter-quarter section (MTRSQQ) centroids. Information on well construction was compiled from California Department of Water Resources Well Completion Reports (CDWR-WCR) included with the PDFs located on the KCPHSD website, or located on the CDWR Well Completion Reports Map Application website. Well construction from CDWR-WCRs was available for 53 of the 71 wells. For one well (Dataset_ID 5), a WCR could not be located, however, well construction information was available in the EWMA GSP. Data were manually compiled into two separate files described as follows: 1) a summary data file that includes well identifiers, location, construction, the number of chemistry samples, the period of record, specific sample dates for each site, and an inventory of which constituent groups were sampled on each date; and 2) a data file of geochemistry analyses for selected constituents classified into one of the following groups: water-quality indicators, major and minor ions, nutrients, trace elements, naturally occurring radioactive material (NORM), and volatile organic compounds (VOCs). Ion (charge) balance calculations and percent error of these calculations were included for samples having a complete suite of major ion analyses. Parameter code, analytical method, reporting level, reporting level type, and supplemental notes were included where available or pertinent. A data dictionary was created to describe the geochemistry data file and is provided with this data release.