"The Real Silent Hill Experience", a collection of various Silent Hill trivia: 
This is actually a supplementary to a much larger project that was posted in 2010 with the intention of providing a down-to-earth, factual synopsis of the series and consequentially clearing up all speculation and inaccuracies residing within the community in regards to the overall story and themes of Silent Hill. Watch the entire three and a half hour long documentary starting with the introduction here. An eye-opening, provocative must-see for all fans of the series and an interesting, clarifying experience for newcomers alike.
Let's Play: Numerous due to the series' popularity. Some notable LPers:
From Earth (1-4), who uses the magic of screenshots to mock every single aspect of the series. At one point in his SH1 LP he confuses Kaufman's dialogue for Harry's, but it works due to the running gag of Harry constantly asking stupid questions.
L0rdVega (1-3), who did blind runs and still somehow managed to beat the games.
Voidburger (1 and Origins), who went above and beyond by going in-depth in various pieces of trivia and exploring the games' extras. Also, Mad Libs notes.
The creators are frustratingly coy about which of the endings are canon. A few of the additional releasesonly available in Japan do shine some light on things, but real answers are as rare as ampoules. (It is canon that Silent Hill 1, 3, and Origins had good ending and heavily implied that "Into the Water" was the bad ending for Silent Hill 2).
Although to many, this simply makes the games more scary, since the games are one of the few instances in media where pretty much everything is symbolic of something. It causes many players to simply speculate even more about the series. Since there is no true answer to many of these questions, it makes the nature of the town that much more unsettling.
The actual location of the towns of Silent Hill, South Ashfield, and Shepherd's Glen are somewhat fuzzy, though some of the extra material makes special mention of the founding of the state of Maine.
In the movie, Silent Hill is very obviously modeled after Centralia, Pennsylvania, where a long-burning coal fire has caused most of the residents to be relocated elsewhere.
The movie version places it in West Virginia.
Shattered Memories uses the 49504 zip code of Grand Rapids, Michigan. And yet there's a street-sign right near Harry's car at the start that says Buffalo and Rochester (both Western NY cities) are less than 70 miles East of where the town is. Then again, the sign is laying on the ground in a junkyard.
The receipt that kicks off the Kaufmann sidequest in the first game mentions a sales tax of either 6.25% or 6.75%. Not very helpful by itself perhaps, but in conjunction with other evidence, it might tell us something.
Many of the cars in Silent Hill 2 and 3 have (admittedly blurry) license plates that resemble Illinois plates.
It is supposed to be in New England, and many fan theories have put it in Maine.
The Official Cannon for Silent Hill is that it is located in Maine, New England; Maine is the most north-eastern state of the United States of America. Although its precise location was ambiguous for a long time, several hints implied Silent Hill to be in Maine throughout the series.
The Japanese publication Book of Lost Memories, as well as the instruction manuals for Silent Hill, Silent Hill Origins and Silent Hill: Homecoming, all have stated that the town is located in New England.
In Silent Hill: Homecoming, there is a book shelf which contains information about mining towns of New England in Shepherd's Glen Town Hall.
Inside of the liner notes for the Japanese release of Silent Hill 4: The Room's soundtrack, an address is given for Heaven's Night that would have placed it in Maine. The state abbreviation for Maine is "ME".
Further information can be found in Silent Hill 3; after Harry Mason left Silent Hill, he and Heather Mason moved to Portland, also sharing its name with Portland, Maine.
In addition, Portland is the hometown to Stephen King. The series has many homages to Stephen King such as "Bachman Road", as well as Carrie and Pet Sematary posters.
In Hiroyuki Owaku's (scenario writer of the first games in the series) Double Under Dusk, Silent Hill is placed in Maine. The two protagonists, Brian and Lindsay, are from Augusta and Orono, respectively.
The Book of Lost Memories' timeline specifically notes "Maine becomes a state."
In the trailer of Silent Hill: Downpour, a bus is seen bearing a Maine license plate.
Additionally, a road sign bears the Interstate 95 logo, a highway that runs through and ends in Maine.
In Downpour, when Murphy Pendleton is about to get on the transfer bus, Anne Cunningham stops him. Her clipboard shows "Maine State Board of Corrections" on it. Interestingly, Stephen King's The Shawshank Redemption is cited as an inspiration for Downpour, and its story is also set in Maine.
The Gillespie House is based on the real life Olson House, which is located in Cushing, Maine.
In Silent Hill: The Novel, Harry feels he should have been enjoying the "Maine wilderness" with his daughter, rather than searching for her.
Doing It for the Art: Every monster in the movie is a person inside a suit, with some CGI effects added afterwards. Unfortunately many people ended up thinking them as shoddy CGI, due to their unnatural movements, which in fact are the result of the skill of their actors, and unusual camera techniques in shooting them; for example, the bubble-head nurses were choreographed doing their movements backwards, and the film was then reversed for the effect.
Executive Meddling: A fairly bizarre example. Sean Bean was cast as Christopher because the studio felt that they needed a male presence in the film, hence why his scenes often seem so disconnected to the main story and they rarely overlap. Ironically, if they simply had kept Harry as the main protagonist and not changed him into the Rose character, this wouldn't have even been a problem at all!
Throw It In: In the film , Colin flicking his tongue in a disturbingly sexual manner wasn't in the script. The actor playing him did it as a joke in one take, but Christoph Gans liked how it looked, so it was kept in.
Uncanny Valley: In the film, the nurses' unsettling movements were achieved by having the dancers/actors perform all the on-screen motions backwards and play them in reverse.
The fact that Silent Hill have direct and indirect connections to various names, plot points, and reported and documents it is unsurprising that Mythology Gags exist in-universe.
It is a known fact that the pattern follows as such (not counting 0 or Book of Memories) - 1, 3, & 6 follow a similar theme set of self discovery, destroying a false god, and a crazy cult while 2, 4, and 5 have their own themes of locating someone lost, finding more about yourself, and saving someone you love. The only difference is that 4 and 6 blends aspects of 2 and 3 and injects it's own new themes. They also all share important character names, places, and dates.
Travis Grady Cameos
A slip of info about him was retroactively added into Silent Hill 2 in the HD collection.
Travis drops Alex Shapard off at his home town in the start of Silent Hill 5 Homecoming.
Travis's truck makes a cameo appearance in Silent Hill 6 Downpour, although Travis himself is nowhere to be found.
During the auditions for Silent Hill 2, Guy Cihi's main reason for being there was that his daughter wanted to try to get the role of Laura. Cihi had some background with acting in high school and college, and he became interested in auditioning for a role. Ultimately, he lands the role of voicing James Sunderland, the game's protagonist!