If you are looking for: please go to:
Historical Mathematics Monographs https://collections.library.cornell.edu/math/
Historical Monographs https://collections.library.cornell.edu/cdl/
Making of America Collection https://collections.library.cornell.edu/moa_new/
New York State Historical Literature https://collections.library.cornell.edu/nys/
Official Records of Union and Confederate Navies https://collections.library.cornell.edu/moa_new/ofre.html
Samuel J. May Anti-Slavery Collection https://rmc.library.cornell.edu/mayantislaverycoll/
War of the Rebellion https://collections.library.cornell.edu/moa_new/waro.html
For all other collections https://newcatalog.library.cornell.edu/digitalcollections