Along with the laptop that Sam owned, the journal was his and Dean's most valuable asset in finding and killing supernatural entities. The journal was John's "single, most valuable possession". The journal is believed to be extensive and is also believed to hold all of the information needed to defeat Azazel whom he had spent his entire hunting career looking for.
Sam and Dean eventually learn that the physical journal itself is actually one ordered by Henry Winchester before he disappeared for his own use. Apparently despite hating the man, for "running out on him," John still kept it and used it for himself when he became a hunter.
On several occasions, it has been shown that the journal actually lacks information on certain things such as John's shtriga hunt and the ghoul hunt that led to him meeting Kate Milligan. In the latter case, the information had been removed to protect Kate and his son Adam, in the former he kept it out of the journal due to how close the shtriga came to killing Sam.
In First Born, the journal is shown to at least in one case, point at John's Lock-Up holding more information on the case referenced in the journal. A "T" in the margin stood for Tara, the hunter John worked the case with.
The journal falls into Mary Winchester's hands upon her resurrection, ten years after Dean inherited it. Mary takes it with her when she leaves and states in Celebrating The Life Of Asa Fox that she used it to retrace John's footsteps a bit. By the time that Mary is trapped in an alternate reality, the Winchesters own it once more.
In later seasons, particularly after they gain access to the Men of Letters bunker, Sam and Dean stop using the journal for information. The last time it is used for information for years is in Season 9's First Born when Dean and Crowley use the journal to find out about John hunting Abaddon's protégé. The journal is briefly seen in Season 12 when its given to Mary, but isn't used for information until Season 13's The Rising Son when Sam looks up the Hell Gate leading to the Shedim and later on, the Princes of Hell. This is a gap of around three and a half years of the Winchesters not using the journal on a case.
- Season 1
- Season 2
- Season 3
- Season 4
- Season 5
- Season 6
- Season 7
- Season 8
- Season 9
- Season 12
- Season 13
- It should be noted that in the published version John states it was given to him by another hunter who told him to write everything down. However, in the show it was originally meant for his father, and John inherited it when Henry disappeared.
- In the animated series, the journal came from John's friend Fletcher.
- John pinned his Marine service medals on the inside cover.
- Following Dean using the journal to find out about Abaddon's protégé in season 9's First Born, the journal did not appear again until it was given to Mary Winchester in season 12's Mamma Mia. However, it was still not used for a case from First Born until season 13's The Rising Son when Sam found information on a Hell Gate Asmodeus was trying to open and later information on the Princes of Hell.
- Prior to season 10, the journal was used at least once a season to help on a case. There ended up being a gap of three whole seasons when the journal was not used to help on cases though it did make cameos in one of those seasons. In the other two, it did not appear at all.
Alex Irvine, in association with Harper-Collins Books, wrote and published the official Supernatural - John Winchester's Journal, also available in E-book format. However it only loosely follows canon.