Oregon and Idaho share a time zone border twice over — Oregon has one county that breaks from the rest of the state, and Idaho is split down its own middle, in a boundary shaped almost entirely by which direction each region's economy actually faces.
Oregon: one county, tied to Idaho instead
Nearly all of Oregon runs on Pacific Time. The exception is Malheur County, tucked into the state's far southeastern corner, which runs on Mountain Time instead — an hour ahead of the rest of Oregon. The reason is straightforward: Malheur County's economy and community ties run east toward Boise, Idaho, far more than west toward Oregon's Pacific-time population centers like Portland or Salem, which are hundreds of miles away across largely rural terrain. Ontario, Malheur County's largest city, sits right on the Idaho border and functions economically as part of the Boise metro area's orbit more than as part of Oregon proper.
Idaho: split down its own middle
Idaho has the opposite problem internally — the state itself is divided between two time zones, not just one border county. Northern Idaho, including Coeur d'Alene, runs on Pacific Time, aligning with Washington state, which it borders and shares much of its economy with. Southern Idaho, including the capital Boise, runs on Mountain Time instead.
The result is a state that's internally split by the same logic that carves out Malheur County next door: Idaho's north and south simply face different directions economically, toward Spokane and the Pacific Northwest in the north, and toward the broader Mountain West (including, conveniently, that same slice of eastern Oregon) in the south.
Two boundaries, one underlying pattern
Line these two up together and a pattern emerges: Malheur County, Oregon and southern Idaho are actually on the same time zone as each other, despite being in different states — while northern Idaho and the rest of Oregon are on a different, shared zone. The state border between Oregon and Idaho cuts across this pattern rather than following it, which is exactly why a single state border ends up being a poor predictor of time zone on either side.
What this means practically
If you're scheduling with someone in Ontario, Oregon, don't assume they're on Pacific Time just because they're in Oregon — they're an hour ahead, matching Boise. And if you're scheduling with someone in Idaho generally, the state name alone doesn't tell you whether they're Pacific (Coeur d'Alene, the north) or Mountain (Boise, the south). The time zone converter resolves both by city, so neither state's internal geography causes a scheduling mixup.
Frequently asked questions
Is Malheur County, Oregon on Mountain Time?
Yes. Malheur County, in Oregon's far southeastern corner, is the one exception to the rest of the state — it runs on Mountain Time (UTC−7/−6), an hour ahead of Pacific. Its economy and community ties run east toward Boise far more than west toward Portland or Salem.
What time zone is Ontario, Oregon in?
Mountain Time, not Pacific. Ontario is Malheur County's largest city, sits right on the Idaho border, and functions economically as part of the Boise metro area's orbit more than as part of Oregon proper. Anyone there is an hour ahead of the rest of Oregon, matching Boise.
Is Idaho in one time zone?
No. Idaho is split. Northern Idaho, including Coeur d'Alene, runs on Pacific Time, aligning with Washington state. Southern Idaho, including the capital Boise, runs on Mountain Time. The boundary runs roughly along the Salmon River, well north of the state's midpoint.
Why doesn't the Oregon–Idaho state line match the time zone line?
Because the zones follow economic direction, not borders. Malheur County and southern Idaho share Mountain Time despite being in different states, while northern Idaho and the rest of Oregon share Pacific. The state border cuts across that pattern, which is why it is a poor predictor of time zone.