Yellowstone County, Montana: drinking water report. Yellowstone County in south-central Montana has about 164,000 residents, with Billings as the county
Yellowstone County in south-central Montana has about 164,000 residents, with Billings as the county seat and the largest city in the state. The Yellowstone River – the longest undammed river in the lower 48 states – provides the primary water source. The Billings area includes two petroleum refineries (CHS Laurel Refinery and Calumet Montana Refining) that process crude oil from the Bakken formation.
The Yellowstone River's undammed status means its flow and quality fluctuate naturally with snowmelt, rainfall, and seasonal patterns. According to Montana DEQ's 2024 water quality report, the river at Billings meets all drinking water source standards, though spring runoff events temporarily increase turbidity and require enhanced treatment. The 2011 ExxonMobil Silvertip pipeline spill released 1,000 barrels of crude oil into the river upstream of Billings, demonstrating the risk pipeline crossings pose to the water supply.
Billings Logan International Airport has documented AFFF use. Montana DEQ's 2024 PFAS investigation found PFOS at 9 ppt in monitoring wells near the facility. The petroleum refineries in Laurel discharge treated wastewater to the Yellowstone River downstream of the Billings intake.
Billings benefits from a river supply that is clean by most measures, but the refinery corridor and pipeline crossings upstream create risk that is difficult to eliminate. The 2011 spill showed how quickly a pipeline failure can threaten the water supply.
Check your water for current data. A carbon filter handles taste and petroleum-related trace compounds. For PFAS, reverse osmosis adds comprehensive protection. Our water filter guide covers both options. Pull your detailed report for trends, and visit our Montana page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Yellowstone County, MT.
The EPA places Yellowstone County, MT in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
49% of homes in Yellowstone County, MT were built before 1980, and 12% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Yellowstone County, MT averages 6.3 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide