Terminal MAIN hosts 8 airlines. It's Alaska Airlines's home turf at SEA.
Gate N1 is still just one security line away from S Gates
SEA calls this whole building the Main Terminal, and every airline here—Alaska, American, Delta, Frontier, Hawaiian, JetBlue, Southwest, United—feeds into the same central security zone before you split off to the A, B, C, D, N, and S concourses. All check-in desks sit landside along the long ticketing hall, so plan 20–30 minutes from curb to TSA at normal times, more like 40+ in the early morning Alaska and Delta bank.
Alaska Airlines uses large chunks of the Main Terminal check-in area and then pushes most flights to the C and N concourses, with some Alaska departures still using D gates during peaks. If you’re checked bags-only with Alaska, the bag-drop kiosks near the C gates security line usually move faster than the general counters closer to the center of the hall.
Delta Air Lines runs its SEA hub from the Main Terminal too, but most Delta departures leave from the A and S concourses, with a smaller group at B. Give yourself at least 15–20 minutes walk time from central security to the far end of S, since you ride the underground train from the Main Terminal to S and then walk another 5–10 minutes to gates like S15–S16.
American, Frontier, Hawaiian, JetBlue, Southwest, and United all check in inside this same Main Terminal ticketing hall, then scatter to A, B, and D gates. United tends to hug the B concourse, Southwest often uses B and D, and Hawaiian flights frequently appear on the A concourse board, so always check the monitor near your airline’s counters before you pick a security queue.
The Club at SEA in the S concourse sells day access, and one FlyerTalk report pegs a three-hour visit at around $50. That lounge sits on the upper level of S, almost side by side with the British Airways Galleries Lounge, and functions as the contract option for IcelandAir, Lufthansa, Condor, ANA, Emirates, and British Airways premium passengers when their flights go out of S gates.
Regulars treat The Club at SEA in S as an “only if you’re already there” stop, not a destination from the Main Terminal core. One frequent flyer even wrote that they “can’t see why it would be worth your time to travel all the way out here,” which lines up with the 10–15 minutes it usually takes to ride the train from central security and walk to the upper-level lounge entrance above S10–S12.
The Main Terminal itself technically has lounges in other concourses—like airline-branded spaces for Alaska and Delta—but the concrete detail here is that the S concourse pair (The Club at SEA and BA Galleries) sit upstairs, away from the main gate level. If your flight leaves from A, B, C, or D, budget an extra 20–25 minutes round-trip if you still want to head to that S-area Club and get back before boarding starts at T-35.
Most complaints about the Main Terminal layout center on the distance to the remote ends of N and S, not on security or check-in. A train ride from the central station near C gates to S, plus the walk to gates S15–S16 at the far end, easily hits 15 minutes in real shoes, so don’t start that trek when your boarding pass already shows “Group 3 boarding” on the screen.
Final tip: at SEA Main, pick your security line based on your actual gate, not your airline—if your Alaska, Delta, or United flight prints a C, D, or N gate, use the checkpoint closest to that concourse and save yourself a 10-minute backtrack after TSA.