This line began in 1846 as the Sandusky, Mansfield and Newark Railroad, running from Sandusky to Newark, Ohio. In 1869, it came under control of the Baltimore and Ohio Railroad, for which it became part of the mainline. In the early 1890s, the B&O began using a new mainline west from Willard, and downgraded this line from its mainline status. It was operated into the late 1970s/early 1980s.
Today, portions of this line remains in operation from Newark to Mount Vernon and from Willard to Mansfield. Elsewhere, the route is abandoned. An 18-mile long rail-trail, the Richland B&O trail, has been constructed on the right-of-way from Butler to Mansfield. Other than that, the line remains undeveloped. An isolated section of abandoned track is still in place as pictured here, just north of Prout. In addition, according to satellite imagery, there appears to be remains of a yard with tracks still in place just to the north of these photos; however, it is now on NASA Plumbrook (government) property.
Thanks to Aaron M. for contributing information about this route.