The Hunters Note is a reminder Bill left on a table in the room at the end of the hall upstairs. Leave his safehouse, go up the stairs, turn right and walk to the last room.
Bill saw a band of hunters getting close to town before a pack of infected chased them away, and he plans to put up more warning signs to show he means business.
Hunters are the armed scavengers Joel and Ellie run into in the next chapter, Pittsburgh.
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.