The extension of spatial and temporal coverage of digital daily maximum and minimum air temperature observations is indispensable for a greater understanding of past climate variability. Long-term series are fundamental for the assessment of frequency, duration, intensity and geographical distribution of past extreme air temperature events at local and regional scales in Ireland. Raw daily observations from 12 long-term and 21 short-term maximum and minimum air temperature series in Ireland, extending from 1831 to 1968, were rescued from multiple archives. Detailed station metadata on instrumentation, site location, observation practices and observer's notes are included in the dataset. Over 970,000 daily maximum and minimum air temperature observations were transcribed from handwritten meteorological registers, publications, newspapers and the Daily Weather Report. The data rescue strategies, sources for data and metadata rescue, and methodologies for double keying are discussed. The Ireland Long-term Maximum and Minimum Air Temperature dataset (ILMMT) format for daily air temperature and metadata and organization is reviewed. The ILMMT dataset comprises raw observations and detailed station metadata, so data users can apply their selected quality control and homogenization approaches.