Mostly Seward, but all of Kenai too:)!
Just a reminder caution that in addition to the normal 4th of July crowds hitting all of the campgrounds and RV Parks (that's everywhere around the big cities regions, and Kenai area gets quite a few people:)!), that Seward also has 'The Race Down The Mountain' adding more to the mix of inbound. So, unless you have a confirmed reservation, I would avoid the Seward area. Most, but not all, of the in town city parks, are full already.
We talked to the Seward City Manager, Jim Hunt, (He had lived in South Dakota for several years, saw our Toads SD plates, and pulled in to talk with us when we were parking in town.) he commented that the first big wave hit Friday and Saturday, with people grabbing spots for the 4th. He said the full spaces open in the parks with water and electric, were mostly filled by Monday afternoon. He said forecasted good weather, will add probably another 5,000 people above the 30-35K that normally visit for The Race Down The Mountain. He said not just the city, but all of the surrounding area, will be 'crazy and swamped' with too many people showing up with no confirmed place to stay.
Also from what I've been able to learn, traveling onto/in Kenai on Thursday and off/out of Kenai Sunday - will be very heavy traffic days. So, we will avoid traveling those days. (We were going to head to Palmer from Seward on Sunday, but will move it out to Monday.)
We ourselves, shifted our confirmed 4th of July reservations in Homer, mad in April, to Seward (We're ahead of schedule, and want to leave time our South travels to visit Jasper and Banf.). We were able to get reservations outside Seward at Stoney Creek RV Park until July 2, and then they have a dry camping 'overflow' area we're confirmed in to Monday AM. Hoping someone will cancel allowing us to stay in the park, as we're enjoying this park.
Best to all, travel safe, have fun - and remember, you might only see the smoke that goes with the BANG - as fireworks are best in the dark...
Smitty