1st and 2nd editions and some supplemental volumes are available for free online:
“The Dictionary of National Biography (or DNB) is a biographical reference for deceased persons notable in British history. The current edition of this work has been published online by Oxford University Press since 2004. The current electronic edition is not free, but is available through individual or library subscription. There is also a recent print edition.
Some earlier editions of this work are freely available online, and remain of historic interest. Below we link to free online volumes of the first and second editions, and some of their supplementary volumes.”
Here’s a link to the Online Books Subject listings:
One of the subject categories is U.S. Regional History, which should prove of some interest to most genealogists…