Official Records - Index or Chapter Locator

The eHistory section of the Department of History of Ohio State University provides HTML versions of the text in Official Records. Some segments are missing, according to that site, but there are quite a few records online. The recordss here are listed by Series, Volume, Part, Serial no., and Campaign.

Department of History, Ohio State University
War of the Rebellion: Index
https://ehistory.osu.edu/books/official-records/index

A Portal to Texas History (site) provides full text of many volumes of the Official Records.
They have a searchbar, but it leads to many, many databases or source books.
A Portal to Texas History

https://texashistory.unt.edu/

I have indexed a few of the volumes and have them listed by volume as individual post titles (see blog sidebar).