The collection consists primarily of letters, short manuscripts, some artwork, and a few proofs of English poets, dramatists, novelists, critics, essayists, biographers, journalists, publishers, artists, and actors who were prominent primarily from the 1890s through the 1930s, collected by O'Connell. Among those represented in the collection are Aubrey Beardsley, Max Beerbohm, John Davidson, Lord Alfred Douglas, Ernest Dowson, John Gray, Maurice Hewlett, Richard Le Gallienne, George Augustus Moore, Stephen Phillips, Bernard Shaw, Arthur Symons, Frederick Wedmore, Oscar Wilde, and W. B. Yeats. The manuscript collection forms part of the larger O'Connell Collection of the 1890s, which contains over 500 printed volumes, among which are many first editions and various periodicals.

The following standard abbreviations, or their variations, are used to identify materials in this collection: ALS = autograph letter signed, TLS = typed letter signed, ACS = autograph card signed, TCS = typed card signed, ANS = autograph note signed, TNS = typed note signed, AMsS = autograph manuscript signed, and TMsS = typed manuscript signed.