Papers of the New York State lawyer, U.S. Congressman (1859-1863), abolitionist, born near Pompey, N.Y. Correspondence (1847-1891); genealogical material; legal and financial records (1814-1879); writings (1837-1884), including essays, speeches, and published letters; and memorabilia. Largely family correspondence with additional letters of Louis Agassiz, Samuel Bowles, Salmon P. Chase, F.J. Child, James Freeman Clarke, Roscoe Conkling, George W. Curtis, John A. Dahlgren, Richard H. Dana, H.L. Dawes, Daniel S. Dickinson, J.T. Fields, John M. Forbes, John C. Frémont, William Lloyd Garrison, George W. Geddes, George F. Hoar, John Jay, Thomas Starr King, Samuel J. May, Robert B. Minturn, Levi P. Morton, Charles Eliot Norton, Elizabeth P. Peabody, Wendell Phillips, William H. Seward, Gerrit Smith, Israel Washburn, R.S. Watson, Andrew D. White, and others.

Correspondence, photographs, journals, clippings, etc. relating to the Porter family of Skaneateles and Lockport, New York, primarily Stanley Porter and Benjamin H. Porter, who served in the Union Navy during the American Civil War. Other family members represented include his parents, James and Sarah, and his siblings Seth and Laura. At one time known as the Mensing-Braun Collection of Civil War Material.

Correspondence, writings, memorabilia pertaining to the American Civil War.