For campgrounds there's the Double J and a KOA on the south side of Springfield. The Double J is on I-55 frontage road which is Old US Route 66. Take I-55 Exit 88. Go west then south on the frontage road about 2 miles. The KOA is the same exit but it's east. The signs are small so watch carefully. It can be hard to find particularly after dark. There's a campground at the State Fairgrounds, some FHU. There is the Riverside Campground just northeast of the Fairgrounds. One problem with the Fairgrounds and Riverside during the summer is they're downwind of Springfield's sewer plant. There are times it can get a bit 'ripe' which blows thru those campgrounds. If there is something going on at the fairground their campground can be full.
If you are looking for a state park type setting then NW of Springfield about 15 miles is Lincoln's New Salem State Historical Site. It has a very nice wooded campground. New Salem is where Lincoln grew up as a young man before moving to Springfield. There's a large reconstructed village of New Salem that's free and well worth the visit. It helps you understand Lincoln's beginnings. Weekends usually have re-enactors dressed in period clothing working around the village. The village is also nice to visit at dusk after everyone has left. You'll see deer and wild turkey roaming the area. During the summer weekends there are usually plays in the theatre at the park. Local performers. Usually well done.
North of New Salem is the town of Petersburg. Several historical Lincoln related sites. One is the burial site of Ann Rutledge who was Lincoln's first love. She died young and many historians believe Lincoln never recovered, caused him to have deep depression his entire life, and affected the way he looked at life in general. The burial site is not Rutledge's true burial. The only thing buried there are a few of her buttons and a few bones. Her true burial site is in a secluded cemetery north of Petersburg a couple of miles. It's along a grass waterway about 1/4 mile off the road in the middle of a farmer's field. It is well maintained and accessible by either driving along the waterway in dry weather or walking. Because the cemetery is away from town many years after Rutledge died the relatives wanted to move her body into Petersburg. Very little was found so Ann is buried in 2 places.
Between New Salem and Springfield is the town of Athens. Visit the Long 9 Museum. It's generally regarded as the unofficial location for the beginning of the Republican Party. The "Long 9" were 9 guys, including Lincoln, who were dissatisfied with the Whig Party, met at the Museum location, and planned strategies. They were called the "Long 9" because like Lincoln they were all taller than average.
For things to see - Of course, Lincoln Presidential Museum. It's not like any other presidential museum. If you just want to take a quick walk thru then plan for at least 4 hrs. You'll leave disappointed that you didn't stay longer. Arrive early and plan to spend the day. Take your time inside and don't miss any of it. It's a mixture of museum and Disney displays.
A 1/2 block south of the Museum on 7th St is the Springfield Visitors Bureau. Stop by there to get maps and info on events.
Lincoln's home is a few blocks south the Museum. It's a National Park. Must see. In the downtown area there are Lincoln's law office and other Lincoln related sites. Visit the Old State Capitol.
On the north end of town is Oak Ridge Cemetery where Lincoln and most of his family are buried. It's the 2nd most visited cemetery in the US behind Arlington. It's a walk thru tomb. Guides will tell the story of Lincoln's first burial location, how tomb raiders tried to dig up and steal his body, and how he is buried now so that no one can ever attempt to steal his body again. One night a week military re-enactors do a lowering of the colors. Nice presentation worth the visit. They give the flag to one of the visitors.
Just a few blocks from Oak Ridge Cemetery is IL's Military Museum at Camp Lincoln, IL National Guard HQ. A hidden gem in Springfield that few visit. A couple of unique exhibits you won't find in any other museum. There's a target that was fired by Lincoln when he was president. A guy named Spencer showed up a the White House with a new rifle he'd invented. He knocked on the White House door and asked the butler to see Lincoln. The called for Lincoln who met the man carrying the rifle. Lincoln called a few others who were in the White House to come along and they went to the area near the Washington Monument, set up targets, and shot the man's new rifle. Lincoln ordered 5000 of them for the Army. Another exhibit is Santa Anna's wooden leg. Santa Anna of the Alamo fame. The IL Militia was deployed to Mexico in search of Santa Anna and they raided his camp early one morning while Santa Anna was still asleep. In Santa Anna's haste to escape he left before he could put on his leg. The IL Militia captured his leg and it's now on display.
About every town in the area has some connection to Lincoln as he traveled extensively as a surveyor, mailman, lawyer, and debate sites when running for president. One of Lincoln's opponents was Stephen Douglas, also an IL person. Most of the presidential debates occurred in IL. 45 miles west of Springfield is Beardstown. That's the site where Lincoln's famous 'almanac' trial was held. Lincoln was representing a man accused of killing another. A witness claimed to recognize the accused in the middle of the night as he was lighted by the light of the full moon. Lincoln used the almanac to show that on the night of the murder there was no moon. About 30 miles SE of Springfield is Taylorville. It's the site of Lincoln's famous "Writ of Quietus" filing. The courthouse at the time was an old wooden building on rock pilings with an open underneath. The buildings were built with open underneaths to aid in air flow for cooling. Pigs would get under the courthouse because it was cooler. During one trial the pigs were making so much noise that Lincoln filed a motion for a "Writ of Quietus" to force the judge to silence the pigs. There's now a statute on the courthouse lawn commemorating the filing.
If you're a Route 66 fan there are lots of Route 66 sites as the route ran right thru Springfield. South of Springfield on the north side of Auburn, IL is the only remaining in-use brick paved stretch of Route 66. It's about 2 miles in length and still used everyday.
A couple of local foods visitors need to try. One is the Cozy Dog. Buzz Waldmire is credited with inventing the dog on a stick. It's not a corn dog. It's a Cozy Dog. The Waldmire family still owns and operates the Cozy Dog which is a Route 66 site.
Another local food is the horseshoe. Smaller portions are called ponyshoes. Texas toast with your choice of meat, or vegetable if you're a vegetarian. Topped with French fries. All that covered with cheese sauce. The cheese sauces vary with each restaurant having their own recipe. D'Arcy's Pint is usually voted as having the best horseshoe. You won't find a restaurant in Springfield that doesn't sell some variation of the horseshoe. Be sure you're really hungry if you order a horseshoe. Usually a ponyshoe is big enough.
If you need more suggestions of things to see and do let me know. You can easily stay busy for a week visiting the sites.
Camped in every state