The substructures were built at two separate times. The stone substructures were built in 1880.
On the west side, spans #1 and #2 are of similar construction. They were both constructed in 1888 for the original two span bridge. Both spans are 103' Pratt Through Trusses with Pin Connections, and 5 panels each. Both have lattice type portals. They are supported by stone substructures.
On the east side, spans #3 and #4 are also of similar construction. Both contain lighter pin connections. Span #3 is 6 panels and 103' while span #4 is 7 panels and 120', with a skewed east end. Both contain a decorative portal bracing. The piers supporting these spans are wooden pile piers. These spans were added after 1919, and were built at at an unknown location in Wisconsin in approximately 1886.
Dates come from the Milwaukee Road Archives at the Milwaukee Central Library
Tony,
Upon field visit, your date may be accurate for the spans, however I don't know if it is accurate for the construction of this bridge in its present form. There are two types of truss spans here, and it appears they may have been built here at different times. Further research will be conducted.
A rather old and lightweight pinned Pratt of 4 spans. Pier is cut stone that has been partially encased in concrete. I think it is safe to say this bridge dates to around 1890.
Perhaps more info found on this bridge:
This photo shows the bridge in the original configuration:
https://www.wisconsinhistory.org/Records/Image/IM84883
Many plans were found for this bridge dated to 1881, but the bridge is dated as 1888/1889 in ICC reports, and is listed as 1888 in an inspection report from 1900.
The eastern two trusses were added in 1931, according to a drawing at the Milwaukee Road Archives at the Milwaukee Central Library: Details of Piers dated Jan. 23, 1931 (found in the Corporate Records; Inspection and Repair of Bridge F-182)
If this is true, it strongly suggests that the two eastern trusses were added this year. Based on other bridges over the Wisconsin River not far from here, these spans were likely built 1885/86.