The Note from Frank is on a table in a house you search with Bill during the High School Escape section. It is in the room closest to where Bill finds his partner, Frank.
Frank tells Bill he is tired of the town and of Bill's stubbornness and wanted more from life. He mentions he finally got the battery Bill kept complaining about.
Frank is dead when you arrive. He was bitten by infected after taking the battery from a military vehicle at the high school, and hanged himself rather than turn. The note admits Bill was right that leaving would kill him, but says he still preferred it to another day with Bill.
Bill's Map
Bill's Map is Bill's hand-annotated map of Lincoln, on a table with an engine near the door you come in through at his safehouse, right after you meet him.
Bombs Note
The Bombs Note is on a table to the left in the side room off the nave of Bill's church. Go into the room on the right, the one Bill makes clear is not the confessional.
Boy's Diary
The Boy's Diary is on the windowsill of a child's bedroom painted with stripes and cars, upstairs in the second house with the dry pool in the new territory beyond the church graveyard.
Fences Note
The Fences Note is another of Bill's reminders, on the table in the back room of his safehouse near the pipe he handcuffs Ellie to.