This map shows the data from https://docs.google.com/spreadsheets/d/1xa0iLqYKz8x9Yc_rfhtmSOJQ2EGgeUVjvV4A8LsIaxY/edit#gid=0 as of 11:30am EST, Jan 28, 2017
Visit the spreadsheet for lots more information on the attendance estimates.

Their notes:

Collection in progress by Jeremy Pressman (@djpressman, U of Connecticut) and Erica Chenoweth (@EricaChenoweth, U of Denver).
With thanks to Rivera Sun, Sarah Syverson, David Luchs, & many others for assistance compiling sources.
We are not collecting this data as part of a research project. We are doing this in the public interest. We are not affiliated with any other efforts to collect data on the demonstrations.

The maintainers of this website theangrygardener@mail.com (mail.com, not gmail.com) are also not affiliated with any other efforts to collect or display data on the demonstrations.