✈️ Flight Guide: Ontario (ONT) → Denver (DEN)

Denver Oktoberfest and numerous fall beer festivals attract visitors in late September into October and can increase demand for ONT→DEN flights and rental cars. Denver also hosts seasonal events like pumpkin patches, brewery tours, and mountain foliage drives in nearby Vail and Breckenridge that peak mid-to-late October. On the Southern California side, Ontario and the Inland Empire have local fall fairs and college events that slightly increase departure-day parking demand. Book travel early if your trip coincides with popular Denver festivals or Colorado leaf-peeping weekends.

For October travel, the best time to fly from Ontario International Airport (ONT) to Denver International Airport (DEN) is mid-week—Tuesdays and Wednesdays—when fares and passenger loads are typically lower. Early-morning departures reduce the chance of cascading delays and can be cheaper, while late-afternoon flights are ideal if you want more relaxed mornings and fewer rush-hour ground traffic issues near ONT. If your trip centers on Denver weekend events or mountain foliage viewing, book at least 4–6 weeks in advance to secure both flights and rental cars.

Nonstop flights from Ontario International Airport (ONT) to Denver International Airport (DEN) save time and reduce the risk of missed connections, making them ideal for weekend trips or short business travel in October. Connecting itineraries may be cheaper—especially if routed through hubs like Phoenix or Los Angeles—but add transfer time and increase the chance of delay. For October travel, choose nonstop when possible for peace of mind around fall weather; if you opt for connecting flights, allow at least 90–120 minutes for domestic connections and avoid tight transfer windows.

Southwest Airlines: Frequently offers nonstop flights ONT→DEN with two free checked bags and flexible change policies, often a top pick for value-conscious October travelers. United Airlines: May offer competitive schedules and loyalty perks (Premier benefits) but often charges for standard checked bags on lower fare classes—good for travelers seeking status benefits or connections. American Airlines and other legacy carriers sometimes provide connecting options via major hubs; these can be cheaper if you’re flexible but riskier during mountain-weather disruptions. For October, compare total trip cost (fare + baggage + seat selection) and choose the carrier that balances convenience and price.

Pack layers for October travel: warm layers, a windproof jacket, and daypack for mountain excursions after arriving at Denver International Airport (DEN). Hydration helps with altitude adjustment when landing in Denver; drink water and limit alcohol the first 24 hours. Check mountain weather before driving on I-70—early-season snow can appear and chain laws may be enforced near mountain passes. At Ontario International Airport (ONT), bring sun protection for Southern California October days and reserve parking early if departing on holiday weekends. Finally, enable flight notifications and have a backup plan for ground transportation if weather delays affect your ONT→DEN itinerary.

Typical nonstop flight time from Ontario International Airport (ONT) to Denver International Airport (DEN) is approximately 1 hour 50 minutes to 2 hours 15 minutes gate-to-gate. Airlines often schedule multiple daily nonstop options—early morning flights (6–9 AM) and afternoon departures (1–4 PM) are common and can be less expensive than peak evening services. In October, schedule reliability is generally good, though occasional mountain weather can slightly increase block time into DEN; always check real-time status on the airline app before heading to ONT.

To find cheap Ontario International Airport (ONT) to Denver International Airport (DEN) flights in October, search early and be flexible with travel days—Tuesdays and Wednesdays often have the lowest fares. Use fare alerts from Google Flights or Skyscanner and set price-drop notifications for ONT→DEN nonstop routes. Consider early-morning or late-evening flights, compare basic economy vs standard fares, and book 3–6 weeks out for the best balance of price and availability. If you want the cheapest option, compare connecting itineraries through Phoenix or Los Angeles, but always weigh additional travel time and transfer risk. Book now to lock in lower October fares and receive updates if prices fall.