At the beginning of this project I hadn't firmly decided to read a book per decade, thinking it would be more one per era or generation. Therefore I did not read anything directly related to the decades of the 1800s or 1810s. In hindsight, I wish I knew more about the times when the first generation born after the Revolution began to grow up and take leadership. Also the War of 1812. It is so glossed over in school, other than the burning of Washington, Dolly Madison saving paintings, and some naval battles.
While they don't count for this chronological undertaking, in recent years I have read biographies of John Adams and James Monroe. For Adams I read McCullough's big seller (and I really enjoyed HBO's miniseries.) But I would just as much recommend learning about Monroe, probably the least known, and youngest, of the Founding Fathers and Presidents considered of that generation.
Gary Hart's take on Monroe got some press because of comparisons he tried to make to contemporary times (hint: G W Bush). They distracted from an otherwise interesting tale with other more relevant lessons.