Daily observations of precipitation and maximum and minimum temperature from the National Weather Service's cooperative observer network collected prior to 1948 were keyed into a digital database. This database includes stations in the nine midwestern states of Illinois, Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, Ohio, and Wisconsin. The primary source used in this project was the publication Climatological Data, which began in 1896. This database provides a substantial enhancement to the National Climatic Data Center's TD-3200 Summary of the Day database, which includes little data prior to 1948. Approximately 2 × 107 data values were keyed, increasing the amount of pre-1948 digital data by about a factor of 3 and substantially improving its spatial uniformity. The data were subjected to an extensive set of quality control procedures. It is expected that these data will find their greatest value in applications requiring very long historical records, such as assessments of the risks of extreme events.