From 1847 to 1859, while Abraham Lincoln was an attorney in Springfield, he rode the Illinois 8th Circuit. About twice a year a group made up of a judge and several attorneys would leave Springfield and ride together to each of the county seats in the central part of state, spending a few days in each to hold trials and conduct judicial business. It was often several days' ride between each county seat.
Seventy years later the Daughters of the American Revolution decided to commemorate Lincoln's circuit riding by placing a plaque at each of the courthouses of the circuit, and also by placing a plaque on each county line on the actual road that Lincoln and his party would follow.
Below is a closeup of one of the plaques:
There were 18 such plaques originally (two have since been destroyed) and each one lists on its base the names of the two counties on whose line it stands. The first one I encountered by chance was on the Coles-Edgar county line. The one pictured below is from the Piatt-Champaign county line plaque.
Interestingly, none of the roads that were used to ride the circuit in the 1850s have evolved into major roads today. All of the plaques are well off the beaten track on two lane, sometimes barely paved, county roads.
I have prepared a map showing the locations of the markers, and of the country seats involved. It is available here. For those especially interested, there is also an excellent article by Guy Fraker about the history of the Lincoln circuit, with descriptions of each plaque's location. The article is available here.