FRA Safety
Tony Howe's mapping effort
LoC Sanborn Maps: 1, 2 3
RailServe, a lot more than just maps, e.g. reporting marks, BRC History
Map Empire including Pam Rietsch's 1895 U.S. Atlas
Harrison Tower
position-light
Brighton Park

Railroad Maps

General

Library of Congress
OpenStreetMap Historic Railways
historic aerials
historical topo maps
USGS's historic topos
4-lane crossings
from Nickle Plate historic site

Towers

Chicago Railfan (Bill Vandervoort)
Ron Roma's
North American Interlockings

Railroads

IC: 1967, 1973, Train Web's, contemporary
Burlington Track Maps
NKP
NSX Heritage, NS interactive, NS layers, NS .pdf, NS corridors
1960 Chicago
history list, specifically Ohio

Chicago

B&OCT
1897 Chicago
2012 IDOT

Illinois

IDOT 2015-16 Secretary of State Digital Archives
Rail System
Rail Plan 2012 .pdf
2012 IDOT, backside
Topos
Walker's SPV Atlases
Carpenter's Rail Atlas in 1946
Illinois Sanborn Fire Insurance Maps COD library number: 21304004559473
Chicago Junctions with Google My Maps
Historical Topos
Aerial
1898
Illinois State Library
1876
south yards details, downloads a .djvu file

Chicago

1897
1916
1920 Chicago & Western Indiana

Indiana

list of links. e.g. Vandalia
Sanborn Maps
Purdue's, has detail inset for East Chicago and Gary
Labeled 2012 INDOT
INDOT, active and abandoned
Allen County
Fort Wayne Interurbans
1999 NS-CSX split
list of maps, "2011 Indiana Railroad Map" is the following
Railfan
Hoosier Valley
Aerial Maps
From IndianaRailroads:
list1
list2
fav1
fav2
fav3
fav4

Iowa

John Smith's list of Sanborn and other fire insurance maps
2013
abandonments

Kansas

Kansas Memory
DOT .pdf
1800s collection

Michigan

Michigan State Rail Plan
Labeled 2007 MDOT
MRA, including details of Detroit
list

Ohio

Freight Rail System Profile (lots of maps)
Toledo, 1951
Toledo, train densities from Rail Fan Guides
abandoned railroads query
Abandoned Toledo Terminal "backside". Has links to Wabash and Cloverleaf Mainline stuff

Pennsylvania

2015DOT