Look at a map of Indiana, and one will notice that the direct route between Centerville and Indianapolis is US 40. While this is true, it is also not entirely so. First, reroutes and bypasses of the old road, especially between Knightstown and Dunreith, have made the route slightly longer. (The above mentioned section can be traveled by the old road, mostly. The Dunreith end has been moved for safety reasons.)
But, there is a second thing to consider here. The first route to connect Indianapolis and Centerville was the Centerville State Road. This road ran slightly south of the path of the future National Road from Greenfield east. This state road was built in 1832 over what was mainly a path. Parts of this route still exist in places. But most of it has been abandoned over the years having been replaced by the National Road in (at least in Hancock County) 1835.
Along the way, some towns just sort of went away because the road went away. There was a village south of Knightstown on the old Centerville State Road called West Liberty. The Indiana Gazetteer of 1833 lists the village as being “on the west bank of the Blue River on the road leading from Centreville (original spelling) to Indianapolis.” That road forms the county line, at that point, between Rush and Henry Counties.
According to an article in the Greenfield Daily Reporter of 08 October 1928, the old state road ran “practically due east and west.” The article goes on to say that the “National Road, although few realize it, veers slightly to the north as it goes eastward.” A quick glance at a map of Indiana, in closer detail, puts the old Centerville State Road on a line basically even with what is now 10th Street in Indianapolis. (Actually, the road that forms the geographic center of Marion County.) Centerville is on a straight line with what would be 25th Street (1.5 miles north). Richmond is on a line that would connect to 30th Street (2 miles north of 10th Street).
With the coming of the National Road, the old road fell into disuse. It would be abandoned in parts, revert to township (and, ultimately, county) control in others. I can’t begin to state with any certainty the route that the old route took to get the 1.5 miles north into Centerville.
Looking at the attached Google map image, the old state road, if it ran true east and west, would be the main street in Milton, Indiana, in the lower left hand corner. Just looking at the map shows a possible route. But since the road was abandoned in places, I am not willing to say with any absolute conviction that that was the road. More research is coming. Who knows, it may end with what George Carlin said his teachers said in class: “it’s a mystery.”