In recent years I just pull it up online to read, as I don't live near a library that has them. Full sets are kind of expensive.
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It is all online to read on Hathi trust, if you scroll down on the page and click on "full view".
Hathitrust: Hay/Nicolay, Lincoln, 10 vols.
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Volume 3 regards the secession crisis, and Volume 4 covers Fort Sumter and the situation at Pensacola.
If you don't like to read book online, you can also listen to it on audio free at Librivox, read by various contributors.
Librivox: Abraham Lincoln; a History, 10 vols.