Ohio State Route 100 is a northwest-southeast route in Seneca and Crawford Counties, with the southern end dipping into the northeastern corner of Marion County. The highway lies at the southern end of north-central Ohio, or at the northern end of central Ohio. The northwestern end is an intersection with Ohio Route 53 in Tiffin, at the center of Seneca County. Ohio Route 100 sets out from there toward Bucyrus. Before it reaches Bucyrus, it picks up Ohio Route 19, which joins it for a long concurrency. That concurrency continues through Bucyrus. Just after passing through town, Ohio Route 19 splits to head more easterly into Galion. Meanwhile, Ohio Route 100 heads a bit more southerly to end at Ohio Route 309. This endpoint is just west of the small town of Iberia.
My photo of Ohio State Route 100 comes from the southern end, at Ohio Route 309. Travelers heading westward on Ohio Route 309, leaving the town of Iberia, will see this guide marker pointing out the right turn onto the start of Ohio Route 100. This photo was taken on the way home from the tour around northeast Ohio in October 2022.