Travelers departing Denver International Airport (DEN) for Ontario International Airport (ONT) in September will find shoulder-season pricing and fewer summer crowds. Early September sees a spike around Labor Day, so book flights to avoid the long weekend or secure flexible fares. Nonstop options commonly operated by United and Southwest provide a roughly 2 hour 15 minute to 2 hour 30 minute flight time; check schedules for midweek savings. Pack layers for Denver's autumn-alike mornings and keep an eye on potential wildfire smoke advisories that can impact visibility and operations. For cheap flights DEN to ONT in September, search Tuesday–Thursday departures, set fare alerts, and consider early morning flights to reduce delay risk. Nearby cities served from DEN include Boulder, Colorado Springs, Aurora, and Fort Collins — useful for planning ground transfers and multi-stop trips.
Arriving at Ontario International Airport (ONT) from Denver International Airport (DEN) in September offers pleasant weather and access to Inland Empire attractions with generally lighter summer crowds. Early September sees event-driven traffic due to the Los Angeles County Fair at the Fairplex in Pomona; factor that into ground transportation plans. Nonstop flights from DEN often land mid-morning or evening — plan ground transfers accordingly. For the best experience, pre-book rental cars if visiting Anaheim or Riverside, or use Metrolink for reliable connections into Los Angeles. Keep an eye on regional air quality advisories in September and consider travel insurance that covers weather- or smoke-related disruptions.
Labor Day (early September) often increases demand on routes from Denver International Airport (DEN) to Ontario International Airport (ONT) as families travel. The Los Angeles County Fair at the Fairplex in Pomona typically occurs in September and drives passenger volume through ONT and nearby airports. Anaheim theme parks see lower crowd levels in mid-September, making it a desirable time for families to visit via ONT. Business conferences in downtown Denver and Southern California can also affect weekday seat availability. Plan travel to avoid major event dates or book earlier to secure best fares.
The best time to fly from Denver International Airport (DEN) to Ontario International Airport (ONT) in September is mid-month on Tuesdays through Thursdays, and during early-morning departures when fares and delays tend to be lower. Avoid peak Labor Day weekend if possible, or book well in advance if you must travel during that time. For business travelers, Monday mornings and Friday evenings can be busier and more expensive, while leisure travelers often find bargains midweek.
Nonstop flights from Denver International Airport (DEN) to Ontario International Airport (ONT) save time (about 2 hours 15–30 minutes airborne) and reduce the risk of missed connections, making them ideal for short trips in September. Connecting flights through hubs like Las Vegas (LAS), Phoenix (PHX), or Los Angeles (LAX) can be cheaper but add connection time and potential disruption. If you prioritize price and can accept longer travel time, a one-stop itinerary may be the best value during September fare sales. Business travelers often prefer nonstop routes for reliability, while leisure travelers shop connecting options for cost savings.
United Airlines: Often offers reliable nonstop service from Denver International Airport (DEN) to Ontario International Airport (ONT) with a strong network connection through DEN. Good for loyalty members and business travelers, with standard checked-bag fees depending on fare class. Southwest Airlines: Popular for domestic DEN→ONT travelers due to competitive pricing, two free checked bags, and frequent nonstop or one-stop options in September. Ideal for families and cost-conscious travelers. American Airlines & Alaska Airlines: May offer one-stop itineraries via their respective hubs (PHX, LAX) that can be cheaper but increase travel time; good options when nonstop seats are sold out. Evaluate total price including baggage and seat selection fees when comparing September fares.
Pack layers for variable temperatures: Denver International Airport (DEN) mornings can be cool in September, while Ontario International Airport (ONT) and Southern California days are typically warm. Bring sunscreen and a light jacket; altitude in Denver can cause stronger sun exposure and dehydration, so hydrate before departure. Be aware of potential wildfire smoke that can reduce visibility and affect health — check AirNow and airline advisories the week of travel. For smoother airport experiences, enroll in TSA PreCheck/CLEAR, prepay parking at DEN if driving, and pre-book rental cars or shuttles at ONT for arrivals during busy fair weekends.
Average nonstop flight time from Denver International Airport (DEN) to Ontario International Airport (ONT) is approximately 2 hours 15 minutes to 2 hours 30 minutes, depending on winds and routing. In September, carriers often maintain regular weekday frequencies with possible adjustments around Labor Day. Early-morning departures can reduce the risk of cascading delays, while evening flights may be subject to higher air traffic into Southern California. Check real-time schedules with your airline 24–72 hours before departure for gate and time confirmations.
To find cheap flights from Denver International Airport (DEN) to Ontario International Airport (ONT) in September, monitor fares 3–6 weeks before departure and target midweek travel (Tuesdays–Thursdays). Use fare-tracking tools and set multi-carrier alerts; consider both nonstop and one-stop options through Las Vegas, Phoenix, or Los Angeles for savings. Flying early morning or late evening often reduces fare and delay exposure. Consider low-cost carriers and loyalty program redemptions for discounted tickets. Compare ONT vs LAX pricing — sometimes flying into Ontario International Airport (ONT) yields lower landing fees and better deals for visits to Anaheim or the Inland Empire.