A statewide observation-well network was developed in Montana in 1947 by the U.S. Geological Survey in cooperation with other Federal and State agencies to provide a long-term record of water levels in selected wells. This report summarized well records and water levels for the network and shows the locations of the wells. Data for 360 wells are tabulated in this report, generally for the period 1985-92. The well records include altitude of land surface, principal aquifer, year of construction, depth of well, primary use of site, primary use of water, casing type,casing depth, casing diameter, top of and bottom of open interval, year water-level data collection began, frequency of water-level data collection, year water-quality data collection began, type of analysis, year water-quality parameter measured, analyzing agency, and type of logs available. The water-level data include date of measurement, water level, method of measurement, and site status. Data for wells equipped with recorders include well number, site identification, name of source agency, well depth, principal aquifer, altitude of land surface, and water level. Well location is shown on a map at a scale of 1:1,000,000.