The introduction to the book details the author's friendship with Henry Sturges. Henry was a frequent customer of his general store, and eventually the two bonded over the author's failed writing career. Then Henry left him a series of books and addresses before leaving. The author later reads the books, believing them to be a hoax...until Henry reveals his vampiric form, as well as something even worse that was sworn to secrecy.
Henry recounting his transformation into a vampire. It turns out he was one of numerous victims of a vampire massacre on the infamous Roanoke Island. The doctor, whom everyone had taken as kind and charming, eventually killed and fed off of everyone on the island before turning Henry out of fear of a lack of companionship. The last we see of Dr. Crowley, he is feeding from a baby. He is not killed for his transgressions, either. At least not in that book. When Henry narrates the Roanoke slaughter in The Last American Vampire, he mentions eventually killing Crowley.
The incidents of Lincoln's life are literal nightmare fuel for him. Two of the four dreams accounted for in the book are not introduced as such, so it seems that Lincoln is truly being suddenly and viciously betrayed by Henry before he wakes up. However, his last dream - detailing a visit to his own funeral in the White House just days before his assassination - is terrifyingly truth in literature.
Jack and Speed are sent to dispatch a vampiric surgeon/professor, Joseph McDowell ([who really existed, by the way). They track him down to a room of glass tubing connected to various living victims, feeding blood constantly to a single source. During the battle, they accidentally destroy the fragile tubing, which shatters all at once sending a rain of blood down upon them.
Examples from the film include:
The scene where Union troops are massacred by the vampire soldiers during the battle of Gettysburg is rather chilling. The vampires are dressed like normal Confederate troops, but as they rush towards the Union lines they begin dropping their rifles, to the bafflement of the Union soldiers, who proceed to fire at the vampires anyway, to no effect. Suddenly the vampires go invisible en masse, and all of the cannons and gunfire go silent; the Union officer is left speechless, and he slowly turns around to see his men already lying dead and the vampire horde charging onward, leaving him as the lone survivor.
This scene also qualifies as a Tear Jerker, with one of the soldiers (a young fellow who is clearly quite green and has no clue what he's doing) kissing a photo of what is presumably his wife... and the next time we see him he's got a hole through his stomach, at which he gasps disbelievingly before keeling over, while the photo falls to the ground, covered in blood.
During Abe's fight with the pharmacist, he falls through a trap door and ends up suspended upside down. He can't reach his axe, and then hears a strange dripping sound. He looks around, quickly realizing he's surrounded by the vampire's previous victims, all of them dangling upside, sliced open, and dripping blood for the kindly seeming old man to harvest.
The flashback to when Adam kills Henry's wife. Henry is in the middle of undergoing a very painful transformation into a vampire as it happens, and is completely helpless to protect her. Not only that, but when Adam bites her throat, he starts spinning her around almost like a dance partner. As they spin, we slowly see the poor woman go from kicking, screaming, and fighting for her life to just hanging limply in Adam's arms.