Background: Older adults in nursing homes (NHs), particularly those with Alzheimer’s disease and related dementias (ADRD), spend most of their time indoors and may be vulnerable to poor indoor environmental quality (IEQ). Multi-pollutant IEQ in U.S. dementia care facilities remain limited. Objectives: To characterize indoor air quality (IAQ), thermal comfort, and ventilation across residential and common rooms in three NHs serving residents with dementia, and to descriptively explore room-level environmental conditions with cognitive status. Methods: TSI AirAssure monitors were deployed in eight residential rooms and five common areas across three Oklahoma NHs (NH-A, NH-B, NH-C) in October 2023 and February 2024. Temperature, relative humidity (RH), CO₂, PM_2.5, PM₁₀, total volatile organic compounds (tVOC), CO, NO₂, and O₃ were recorded at 1- or 15-minute intervals. Ventilation rates (air changes per hour, ACH) were estimated from CO₂ decay curves. Residents’ cognitive status, depression scores, and clinical diagnoses were abstracted from the Minimum Data Set (MDS). Results: Temperature and RH generally met ASHRAE 55 guidelines, though the winter-monitored facility showed low-humidity exceedances. CO₂ concentrations were predominantly below the 1000 ppm ASHRAE 62.1 threshold, although one residential room in NH-C exceeded this guideline 29.9% of the time. tVOC exceeded the Comité Européen action level (0.4 mg m⁻³) across 19.2%–100% of observations in every monitored location. PM_2.5 and PM₁₀ were generally low, with short duration spikes in several rooms in NH-B. Estimated ventilation rates ranged from 0.84 to 5.07 ACH. Conclusions: This pilot multi-facility assessment identifies IEQ concerns in Oklahoma NHs serving residents with dementia, particularly elevated tVOC levels, winter-season low humidity, and low estimated ventilation in selected rooms. The findings support targeted source control, humidity, ventilation, and motivate larger longitudinal studies to evaluate whether chronic indoor environmental exposures are related to cognitive or behavioral outcomes in this vulnerable population.