Finding primary sources in the Theodore Roosevelt Collection sometimes requires using secondary sources to find out more information about the people, events, and other subjects that you're researching. A selection of useful resources is listed here.
Theodore Roosevelt Center: An invaluable database of digitized primary source material by and relating to TR from Harvard, the Library of Congress, and many other collections. Fully searchable (and more user-friendly than Harvard's sites.) In addition to documents, it includes resources on various topics, timelines, quotations, and more.
Theodore Roosevelt Cyclopedia: An index of resources on a variety of topics associated with TR.