This dataset provides chironomid count data and loss-on-ignition measurements for a short sediment record from lake Lontjørnane, located in the Røldal region, Norway. The core spans 33cm and dates from ca 1175 CE to the present. We obtained a sediment core from the centre of the lake (8.8 m water depth) using a HON/Kajak gravity corer during fieldwork in September 2019, and subdivided the core into 1-cm-thick samples in the field. Samples were transported to the laboratory (Birkbeck University of London, UK), where they were weighted and processed using standard protocols – this involved 20 min treatment with warm KOH (10 %) and sieving over a 100 µm mesh. Chironomid head capsules were subsequently handpicked from the residue, mounted on permanent microscope slides, and identified using Brooks et al. (2007). This dataset provides chironomid count data in number of chironomid head capsules per sample. Additionally, loss-on-ignition was determined for each sample by comparing the dry weight of the sample before and after combustion at 550 °C following Heiri et al. (2001). The chironomid dataset provides insight in centennial-scale changes in the insect community of the lake ecosystem under past climate change and current anthropogenic impact.