The Windham County Historical Society was founded in July 1935 at Mortlake, the summer home of Mrs. Theodore Roosevelt in Brooklyn, Connecticut. Its purpose was to encourage the study and collection of all types of material and information of historical value to Windham County.
The collection consists chiefly of letters to Winkler, Elisa von der Recke, and others. Also included are manuscripts of some original poems, a few printed works by and about Winkler, copies of documents pertaining to Winkler's family, including Festschriften in his honor, and photographic reproductions of portraits and drawings. Correspondents include H. C. (Hans Christian) Andersen, Sarah Austin, Ludwig Börne, Eduard Devrient, Johann Peter Eckermann, Paul Johann Anselm Ritter von Feuerbach, Christian Fürchtegott Gellert, Johann Wilhelm Ludewig Gleim, Ottilie von Goethe, Karl Gutzkow, E. T. A. Hoffman, August Wilhelm Iffland, Friedrich Maximilian Klinger, August von Kotzebue, Johann Caspar Lavater, Charles Joseph, prince de Ligne, Schnorr von Carolsfeld, Ludwig Tieck, Carl Maria von Weber.