This information came from Tim Stowell, the Wisconsin co-cordinator.
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The abbreviation (ch) stands for courthouse. The 1939 reference is a
United States Official Postal Guide - Part 1 - July 1939 - 5th Series - Vol
2, No. 1. I (Tim) picked it up at the World's Longest Yard Sale a few years ago
for 25 cents.
The 1886 reference is missing its cover and first 13 pages so it's a bit of
a mystery. It appears to have been published by an independent
organization as it has advertisements in the back of the book.
In 1886 there were 1,478 postoffices in Wisconsin.
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Lincoln County Postoffices in 1886
Bismarck
Bloomville
Champagne
Chat
Corning
Donovan
Dudley
Eagle River
Grandmother Falls
Merrill (ch)
Rhinelander
Merrill and Rhinelander were identified as Money Order offices. Merrill
was further identified as an International Money Order office.
Lincoln County Post Offices in 1939
Doering - P7
Gleason - R476 P31
Heafford Junction - P37
Irma - R254 P23
Merrill (ch) - R1343
Spirit Falls - P10
Tomahawk - R370 S305
R - boxes on rural routes emanating therefrom
P - post-office boxes at offices not having city letter-carrier service
S - boxes on star routes emanating therefrom