The scene where President Lincoln works at a large Oval Office desk while his son Willie plays with toys beneath it, is based on an iconic photograph of President John F. Kennedy and little John Kennedy Jr.
When Adam bites Henry, Rufus Sewell had never played a vampire before. No one had given him "the talk" on how to perform a vampire bite which led to him accidentally breaking his fake vampire teeth. They were longer than he had realized.
Joshua Speed (played by Jimmi Simpson) was one of Abraham Lincoln's oldest friends dating back to their days in Springfield, Illinois. Although Joshua never actually came to Washington his brother James Speed was considered one of Lincoln's oldest friends in Washington and served as Attorney General from late 1864 until he resigned in 1866.
Several times through the course of his early training, Lincoln sustains wounds to his right eye. This is a possible reference to actual future events. When Booth shot Lincoln at Ford's Theater, the bullet lodged just behind his right eye.
Trent Reznor was approached about scoring and playing a minor part in the film, but the news leaked before the final decision and Reznor voted to pass on the project as the surprise element of his participation had already been lost.
Benjamin Walker previously appeared, in 2010, in a stage production called "Bloody Bloody Andrew Jackson." In both that play and this film, he plays a title character who is a fantasy version of a real-life American President.
The trivia items below may give away important plot points.
At the end of the film, when Lincoln says goodbye to Henry, his wife Mary called him saying that they will be late for the theater. That theater excursion was the last made by Abraham Lincoln, who was assassinated in Ford's Theatre in Washington by John Wilkes Booth on April 14, 1865, dying in a coma at 7:22 the next morning.
Although both are credited to the same author Seth Grahame-Smith, the book and movie sharing the title "Abraham Lincoln: Vampire Hunter" are very different. Adam and Vadoma do not appear in the book - they were created to satisfy the fantasy-action movie tradition's demand an "archnemesis". In the book Henry was born in the 1500s and Abe recognizes him as a vampire at first sight. Vampiric twists are given to many well-known trivial anecdotes from Abe's biography, as well as additional Civil War battles such as Bull Run and Antietam. There are tangential subplots involving historical figures such as Edgar Allan Poe, William Henry Seward, General George B. McClellan, and John Wilkes Booth. (The movie's inclusion of Harriet Tubman, who was not in the book, may attempt to compensate for this loss.) Mary Todd Lincoln never learns about vampires. Vampires are able to kill other vampires, and there are many "vamp on vamp" battles whose absence is considered by book fans to be one of the film's largest shortcomings. There is also a surprising twist at the end.
Seth Grahame-Smith, who wrote both the screenplay and the novel on which the movie is based, explained to Time Magazine that (contrary to many audience members' assumptions) the text-sending man in the bar, whom Henry recruits as his latest partner at the end of the movie, was not meant to be George W. Bush, Barack Obama, or any other real-life public figure. It's just the average man. To quote: "It's not meant to be anyone particular, it's just meant to sort of dovetail with the earlier scene of Henry and Abe." He also said that he himself played the texting man.