Calvin Coolidge Presidential Foundation: Coolidge Virtual Library
Digital Public Library of America: Progressive Era, 1900--1930
Library of Congress: America at Work, America at Leisure, 1894--1915
Library of Congress: Progressive Era to New Era, 1900--1929
National Archives: Milestone Documents: 16th Amendment to the United States Constitution: Federal Income Tax (1913)
National Archives: Milestone Documents: 17th Amendment to the United States Constitution: Direct Election of U.S. Senators (1913)
Library of Congress: 18th Amendment to the United States Constitution: Prohibition
National Archives: Milestone Documents: 19th Amendment to the United States Constitution: Women's Right to Vote (1920)
Library of Congress: Child Labor & Lewis Hine Photography Collection, 1908--1924
Berkeley Library, University of California: Suffragists Oral Histories
Digital Library of America: Women's Suffrage: Campaign for the 19th Amendment
Library of Congress: Elizabeth Cady Stanton Papers
Library of Congress: National American Woman Suffrage Association Records
National Archives: Woman Suffrage and the 19th Amendment
Digital Library of America: Women and the Temperance Movement
Teach US History.org: The Second Great Awakening and the Age of Reform NOTE: Some of these sources are pre-Progressive Era; watch your dates carefully when selecting a source!
Westerville Public Library: Anti-Saloon League Collection
Digital Public Library of America: Environmental Preservation in the Progressive Era