•Well-supported cognitively unimpaired plasma NfL reference intervals were determined.•Observed 97.5th percentile NfL concentrations increased at a rate of 3.1% per year of age.•Decade-wide reference intervals will aid in the evaluation of potential neurodegeneration. Neurofilament light chain (NfL) is an emerging biomarker of neurodegenerative disease progression. As plasma NfL increases with age, characterization of NfL concentrations in an age-stratified cognitively unimpaired population was assessed. EDTA-plasma samples were measured using the Simoa® NF-light™ Advantage Kit assay. One-sided reference intervals were established from 1100 cognitive normal individuals (588 male, 512 female) aged 20 to 95 years. Of those, 927 samples were obtained from the Mayo Clinic Study of Aging cohort (age > 50 years), and the remainder (age < 50 years) were obtained from individuals without known neurological conditions. All samples were from individuals without known chronic kidney disease, stroke or myocardial infarction, and a body mass index < 30 kg/m2. The 97.5th percentile limits for the following age ranges (in years) were (pg/mL): 20 s: ≤8.4, 30 s: ≤11.4, 40 s: ≤15.4, 50 s: ≤20.8, 60 s: ≤28.0, 70 s: ≤37.9, 80+: ≤51.2. Sex had no significant effect on reference intervals. Observed NfL concentrations increased at a rate of 3.1 % per year of age. Characterization of the rate of NfL concentration increase and decade-wide reference intervals from a neurologically well-characterized patient population will aid in interpretation of NfL during the clinical evaluation of a potential neurodegenerative disease.