Bridge was replaced in 2007 with a replica
Based on photos in link and uncertanty surrounding bridge design, and the key stone design, this was almost certainly a former railroad. A C&NW map (which I can no longer find) showed the line had weaved back and forth around here, and was sold to the county upon a new line being constructed in 1899.
If this is the case, there may be similar bridges still in existence on Chatfield Road (county 51) around here. It has been a couple years since I was back here, but there are many creeks and possible sites for more.