I live in SW Michigan and have known of legit 8 plus Bass being caught and yes weighed on an accurate scale, not a common occurrence but they are there in our part of the country and I would imagine in Illinois as well . In my opinion in this part of the country when fishing for largemouth on our inland lakes in most of our lakes you've caught one of the biggest oldest Bass in the system when you run into a 6 lb plus fish .
I don't claim to be God's gift to fishing but because of time on the water & opportunity I've been fortunate to have caught more than my fair share of the 5 plus Bass the past 20 years or so with a decent number of those 6 lb plus fish as well. So I will share my observations on what has worked for me which I think would be pretty applicable to the OP fishing in Illinois since it's in the same part of the country.
As others have pointed out location & presentation are by far the most important ingredients to catching bigger fish whether a big fish in your part of country is 6 lbs or you live in an area where 10 lbers are big fish. This will always apply no matter where you fish or even what you fish for.
There is no doubt that average size baits or on occasion tiny baits will catch trophy class fish . That said If 2 fisherman of similar ability were fishing a season at the same lakes with a Crappie jig verses a medium to large size swimbait I'm confident the swimbait fisherman will likely catch a lot more of the bigger fish that are available in their area.
Though I'm a believer in swimbaits I have also have had success with conventional tackle which is what I 've cut my teeth with and still use as an integral part of my fishing. Though I don't believe this applies as much with small mouth I tend to do better using larger versions of these baits in most situations though they don't have to be huge to be effective. As an example , when using a walking stick bait I tend do better with a 5" bait verses a 3 " walking bait. My favorite size of the Whopper Plopper is the 130 , not a huge bait but it catches almost as many as the smaller versions but my average size fish tend to be a lot bigger and more likely to catch a 5 plus Bass in my opinion. When slow rolling a Kietech or a hollow belly on a jighead in deep water I tend to do much better with say 4.8 or larger size verses the 2.8 as another example .
In the category of conventional tackle Jigs have been my most consistent producer of bigger fish but really just about all the major category of lures will produce at the right time. Deep diving cranks in the summer are probably a close second.
So I definitely still use conventional tackle. However , there is a place for big baits even in Northern states and at times they can be special and a blast to fish. Keep in mind if you are price conscious and have a limited amount of discretionary income they may not be right for you. Also, you will need to be bullheaded and be willing to go through a learning curve with these baits and if you can only fish once a week for about 3 hours it probably won't be worth it . That said if you are already a successful fisherman with conventional tackle then it can be an exciting addition to your arsenal. If someone is still a novice fisherman then start of with conventional tackle and learn the fundamentals before you even think about fishing larger swimbaits .
The cool thing about adding this category of lures to your arsenal is that it is a great way to show the fish on heavily fished lakes something different and even when they are not getting bit they will show big fish. They also tend to catch nice bonus fish , especially on lakes where Muskies are available. Even when Muskies are not part of the system they tend to attract bigger Pike over those pesky hammer handles. Big Walleye also like these baits.
On a lot of our inland small lakes especially the smaller ones under 500 acres Bluegills and Perch often times are the dominant forage so don't believe those who say you should only throw Bluegill swimbaits in the spring. There have been some real nice Bass that I 've caught in the summer & fall that will argue otherwise. In addition to Bluegill & Perch I also like Golden Shiner, Baby Bass, Carp patterns and even Trout colors on non Trout lakes.
So here some of the baits that I'm confident will produce...
Topwater Wake style baits - The 7 " & 9" MS Slammer & Spro Rat 50 size are readily available and work well especially at night or low light conditions. That said I love the 3:16 Wake Jr. , the problem is they are expensive and hard to get. The best way is through the buy/sell pages of the swimbait forums. They are a special bait when used in the right situation.
Bluegill style topwater bait. - The Matt lures Hardgill is an awesome bait , it will flat out catch numbers and big ones as well. I absolutely love this bait and it will work in shallow water when the others get ignored. Besides a slow steady retrieve try mixing in shorts rips. Think prop bait without a prop. The Got' em Coach Gill can be had for a reasonable price and had produced a 7lber for me a few years back. I tend to use the Matt LURES when I want to finnesse the fish more and go the GEC when I want to fish a little more aggressively.
Glide baits - The River to Sea S Waver 168 & 200 size. Don't waste your time with the smaller sizes. The Gancraft 178 Jointed Claw in the Perch color is one of my favorites and are readily available like the RTS baits though they are pricier. That said shad/ golden shiner profiles have been very good to me especially in the spring. One bait that doesn't get talked about but has been very good to me is the Evergreen ES Flat, you can usually find them on Ebay and they aren't terribly expensive. Last year was my first with the High Power Herring 8" glide bait. I'm very impressed with this bait though I did much better fishing fairly fast with quick stop and go turns of the real handle and jerking the slack. That said if you want one they are fairly hard to get and expensive. You will also hear a lot of recommendations for a Deps 250 , for whatever reason I have not caught any on this bait but it's success throughout the country speaks to it's abilities I just need more time with it.
Crank down bait - the Pat's Perch is a great bait. I was lucky enough to get a few before they became hard to get and very expensive . I caught some on the Bull Shad 4 x 4 last year though I need more time with the bait. It is more readily available and affordable than the Pat's bait. A lure that I 've experimented with last year is the Musky Armour Krisco Jr which caught me enough fish last year to make want to give it more time on the water next spring. It is mass produced and under 20 $ so it might be worth a shot . Though these are crankbaits the Rapala Super Shad Rap and especially the Strike King Mag 8.0 squarebill will catch big fish. I love that SK 8.0 squarebill .
Multi Joint sinking baits. - some of the ones that have excelled for me include are the sinking versions of the Matt's Hard Gills, Bull Shads & Bull Gills also produce. The Jackall Ganteral would be a great bait to start with as it's readily available with an affordable by swimbait standards price tag. Fish these baits, sometimes slow or even twitch them.
If I had to sell them all and can only keep one it would be the 7" 22nd Century Trout in the Baby Bass color. It was already one of my better swimbaits before I knew what I was doing with it as it will produce with a steady retrieve. That said when I started fishing it with a stop & go fast retrieve along with some twitches then it became my favorite hard bait style swimbait. That said don't over do the twitches as the line can wrap around the hook as it is a lipless bait. Think of this as combo swim & jerk bait and it will absolutely produce. These tend to be a medium priced for swimbaits but the good news is they are not hard to get.
Soft swimbaits are also a staple of swimbait fishing , especially when dealing with grass or cooler water. Slow rolling heavier style Hudd baits , kietech/ bass trix style baits attached to jigheads are also a great way to have fun swimbait fishing. I've had bass as small as 2-1/2 to 3 lbs choke on an 8" Hudd so don't be afraid to try these baits. If you made it this far and due to the length of my post I will stop right here . This is a terrific website and at times has good info for swimbait fishing, that said I think the majority of the info and fisherman on this site tend to rely more conventional tackle which should be the foundation of any Bass fisherman . I would also suggest you that if the OP was interested in swimbait specific info that he may also want to check out some speciality swimbait sites in addition to the great info on Bass Resource.