Washington Street Bridge (Old)
Photo from old postcard
BH Photo #512874
The more I study these photos the more I believe the problem may lie with the colorization that was done on them. It is highly plausible that the artist may have only noticed the one counter and thus only chose to highlight it. Thinking of a Parker truss of this size, it would be highly unlikely (and of questionable design) that there would not have been counters in at least the two central panels. And there certainly would NOT have been only one counter in a 14-panel truss. I do think they were likely present on the image of the Monroe Street span, but were faint and not highlighted in the postcard.
That being said, I would tend to agree that this very well could be another image of the Monroe Street Bridge.
I'm tending to agree with Paul, mainly based on that distinct house. If I hear more from you guys, I'll move the postcard pic.
It looks like 14 panels to me, but as you say it is indistinct on the left side and hard to tell for sure. I've been staring at the photos of both bridges and I think the Monroe span does have counters in the eighth panel from the right (oddly asymmetrical), which is the same panel as the "X" in the photo on this page. I haven't been able to find a good photo that is definitely Washington Street though so I'm still not sure either way.
The only thing that keeps me from agreeing with you is the single X panel seen on this bridge. It's hard to clearly count the panels on the Left side, so could this have actually been a 15-panel truss? On the Monroe Street Bridge counters appear to have been omitted altogether. That being said, I don't see any writing on the postcard which makes me wonder if this bridge might have been placed at the wrong location. It appears that Tiffin had numerous crossings of the Sandusky within the city, so it would take some more digging to sort this out.
I may be wrong, but I have a hunch that the postcard photo on this page is actually the Monroe Street Bridge for the following reasons:
1) Same number of panels, same design. An Images of America book that I have has a photo after the 1913 flood showing a stone pier at Washington Street, indicating that a two-span bridge stood there.
2) In the photo on this page, I notice a house with a barn-shaped roof on the right side. Either this house or one pretty similar still stands today at the end of Monroe Street: https://firstname.lastname@example.org,-83.1784427,3a,90y,31...
3) A two-span truss bridge is visible in the background of the photo on this page. If this is really the Washington St Bridge, then the background bridge would have to be the railroad bridge. However, although admittedly it is hard to tell for sure, the two bridges appear to be parallel, whereas the RR bridge actually crosses the Sandusky at quite a different angle than the Washington St Bridge. If the Parker truss is the Monroe Street span, then the bridge in the background could be the parallel Washington St. bridge.
Additionally, the Facebook photo in the source link looks like it might show a Whipple truss on Washington Street rather than a Parker.