The recent round of day-by-day excerpts of The First Assassin brings to mind one of the vital sources of the novel: a three-volume set of books called Lincoln Day By Day, written by C. Percy Powell and published by the Lincoln Sesquicentennial Commission in 1960. It describes what Lincoln did on each day of his life, based on historical records. The early years are full of gaps and the professional years are full of legal work, when he argued cases, reached settlements, etc.
The third volume covers the Civil War years. I made extensive use of a copy at the Library of Congress, wanting to make sure that my character Lincoln always was located where the historical Lincoln spent his time on certain dates. Thirty pages of it, copied from the edition at the Library of Congress, have sat in my filing cabinet for years. Nowadays, however, the whole thing is online. It’s called the Lincoln Log.