Street's papers on Theodore Roosevelt are composed of correspondence, the majority being letters from Roosevelt to Street, as well as copies of articles, clippings, and other related materials which Street collected and prepared for a book of manuscript materials documenting his association with Roosevelt. Also included are Street's title pages for each section and descriptions by Street of most documents that provide explanations of references within the letters and related events.

Initially, the majority of the correspondence is concerned with articles by Street about Roosevelt, including "The Most Interesting American," and also includes copies of those articles. This type of material is found throughout the papers. Beginning in October 1915, other correspondence concerns invitations to Street for social visits with the Roosevelts. Their correspondence also includes frequent mentions about Roosevelt's views on the nation's preparedness for war, the need for the United States to enter World War I, and criticisms of Wilson's policies to stay out of the war. Other subjects of conversation include the Republican National Convention in 1916 and the campaign of John Purroy Mitchel for New York mayor in 1917. Additionally, the papers include correspondence from Edith Roosevelt, typically brief acknowledgements of gifts Street sent them or of visits.

The papers also contain materials related to Roosevelt's death in 1919. These include Street's reflections upon Roosevelt's last days and a memorial article he wrote for Collier's. It also includes several articles written by others who knew Roosevelt about his legacy, and correspondence between Street and political, military, and literary figures about Roosevelt, the leadership of the Republican Party, and contributing materials for this book of manuscripts that Street was compiling. Also included are photographs of Roosevelt delivering speeches, with family, friends, and political and military figures, images of his home, portraits, and images of his funeral.