List of protests in the United States by size
List

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Protest
City
Estimated participants
Date
Image
1
2017 Women's March
—
3,300,000–4,600,000
January 21, 2017
-
2
2018 Women's March
—
1,500,000
January 20, 2018
2018 Women's March in New York City
3
March for Our Lives
—
1,200,000-2,000,000
March 24, 2018
Protesters in Washington, D.C., 2018
4
March for Science
—
~1,000,000
April 22, 2017
Protesters in Washington, D.C., 2017
5
March on Washington for Lesbian, Gay and Bi Equal Rights and Liberation
Washington, D.C.
800,000–1,000,000
April 25, 1993
Demonstrators in front of the White House
6
Anti-nuclear weapon march, part of the Nuclear Freeze campaign
New York City
700,000–1,000,000
June 12, 1982
-
7
Million Man March
Washington, D.C.
670,000–800,000
October 16, 1995
-
8
March for Women's Lives
Washington, D.C.
500,000–1,000,000
April 25, 2004
-
9
Million Mom March
Washington, D.C.
750,000
May 14, 2000
-
10
March for Life
Washington, D.C.
400,000-650,000 (2013 estimate from rally organizers)
Annually since January 22, 1974
2013 march
11
Million Woman March
Philadelphia
500,000
October 25, 1997
-
12
Moratorium to End the War in Vietnam
Washington, D.C.
500,000
November 15, 1969
-
13
People's Climate March
New York City
311,000–400,000
September 21, 2014
-
14
March on Washington for Jobs and Freedom
Washington, D.C.
250,000–300,000
August 28, 1963
-
15
Solidarity Day march
Washington, D.C.
250,000–260,000
September 19, 1981
-
16
February 15 Iraq war protests
New York City
200,000–375,000
February 15, 2003
-
17
Rally to Restore Sanity and/or Fear
Washington, D.C.
215,000
October 30, 2010
-
18
March on Washington for Lesbian and Gay Rights
Washington, D.C.
200,000
October 11, 1987
Nancy Pelosi participating in the march
19
2015 Armenian March for Justice
Los Angeles
130,000+
April 24, 2015
Armenian genocide massive march in LA.JPG

Question: Which major US protests were not centralized to a specific city?
Answer: March for Our Lives, the 2017 and 2018 Women's Marches, and the March for Science are some of the largest protests in American history without a single location.