This publication provides digital flight line data for a high-resolution horizontal magnetic gradient and radiometric survey over an area of southeast Missouri and western Illinois. The survey represents the first airborne geophysical survey conducted as part of the U.S. Geological Survey (USGS) Earth Mapping Resource Initiative (Earth MRI) effort (Day, 2019). Earth MRI is a cooperative effort between the USGS, the Association of American State Geologists, and other Federal, State, and private sector organizations to improve our knowledge of the geologic framework of the United States. Data for this survey were collected by Terraquest, Ltd. under contract with the USGS using a fixed wing aircraft with magnetometers mounted in the tail stinger and each wing tip pod and a fully calibrated gamma ray spectrometer. The survey operated out of the Farmington, Missouri airport from December of 2018 to May of 2019. The survey covers a 146-kilometer x 154-kilometer area centered on the town of Ironton, Missouri. Data were collected along north-south flight lines spaced 300 meters (m) apart with east-west tie lines flown every 3000 m. A mean terrain clearance of 117 m was maintained except where safety dictated a higher elevation. A total of 68,375-line kilometers (km) of data were collected. Files that are available in this publication include flight line data for the magnetic gradient survey, flight line data for the radiometric survey and a report describing the survey parameters, field operations, quality control and data reduction procedures. A zip file is provided that contains the contractor's deliverable products that includes Geosoft databases and grids for the magnetic and radiometric survey and the report describing the survey and data reduction. The 2018-2019 survey was designed to augment and connect two previous USGS airborne geophysical surveys. Adjacent surveys include a magnetic and gravity gradiometry helicopter survey flown in 2014 (McCafferty, 2016a) centered on the Pea Ridge iron mine and a magnetic and radiometric survey flown in 2016 and centered on Ironton, Missouri (McCafferty, 2016b). References cited Day, W.D., 2019, The Earth Mapping Resources Initiative (Earth MRI): Mapping the nation's critical mineral resources: U.S. Geological Survey Fact Sheet 2019-3007, https://doi.org/10.3133/fs20193007. McCafferty, Anne E., 2016, Helicopter magnetic and gravity gradiometry survey over the Pea Ridge iron mine and surrounding area, southeast Missouri, 2014: U.S. Geological Survey data release, https://doi.org/10.5066/F78P5XM4. McCafferty, A.E., 2016, Airborne magnetic and radiometric survey, Ironton, Missouri area: U.S. Geological Survey data release, https://doi.org/10.5066/F7B56GT8.