The GPM Ground Validation Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) OLYMPEX dataset consists of brightness temperatures from 9 channels as measured by CoSMIR when flown on the NASA DC-8 aircraft during the Global Precipitation Mission (GPM) Olympic Mountains Experiment (OLYMPEX) campaign. CoSMIR is a conical and cross-track scanning radiometer with frequencies centered at 50.3, 52.8, 89.0, 165.5, 183.31+/-1, 183.31+/-3, and 183.31+/-7 GHz. Data files are available from November 5, 2015 thru December 19, 2015 in HDF-5 format, with browse imagery files in PNG format containing brightness temperature time series plots.