Htydjtk

I always wondered when the setting of the books was supposed to be. Is it set in the past? Present? Future?

I remember seeing somewhere that there was actual years/dates associated with events in the book.

Is there a visual timeline of all the Harry Potter events somewhere with years/months/days mentioned?

All dates in the HP world trace back to the Death Day party of Nearly Headless Nick in The Chamber of Secrets. It was stated that his it was his 500th Death Day. The cake reads:

Sir Nicholas de Mimsy-Porpington

died 31st October, 1492

So, it stands to reason that during the second year, Harry Potter was 12, and that it was the year 1992. All dates can be calculated from that moment in time.

It should also be noted that this isn't strictly adhered to, specifically, Dudley has Playstation before they came out, among other things.

Harry Potter was born 31 July, 1980, and entered Hogwarts in 1991.

Source: The Harry Potter Wiki.

Generally accepted answer: The books take place between 1991 and 1997

Evidence: 

• 
  

  Nearly-Headless Nick's 500th deathday party in book two has a cake with the words:

  
  
  

  
  

  Sir Nicholas de Mimsy-Porpington died 31st October, 1492
  _{(Harry Potter and the Chamber of Secrets - Chapter 8)}

  
  

  
  


• 
  

  Harry's parents died in 1981

  
  
  

  
  

  JAMES POTTER
  
  BORN 27 MARCH 1960
  
  DIED 31 OCTOBER 1981

  
  
  

  LILLY POTTER
  
  BORN 30 JANUARY 1960
  
  DIED 31 OCTOBER 1981
  The last enemy that shall be destroyed is death.
  _{(Harry Potter and the Deathly Hallows - Chapter 16)}

  
  

  
  


• 
  

  J K Rowling's old website

  
  
  

  
  

  Harry Potter (1980 - )
  
  The Boy Who Lived, only known survivor of the Avada Kedavra curse and conqueror of Lord Voldemort, also known as Tom Riddle. Harry Potter joined the reshuffled Auror Department under Kingsley Shacklebolt at age 17, rising to become Head of said department in 2007.
  Albus Dumbledore 1881 - 1996
  
  Brilliant and often controversial headmaster of Hogwarts School of Witchcraft and Wizardry, Albus Dumbledore is most famous for his 1945 defeat of Grindelwald and his steadfast championing of Harry Potter, the Boy Who Lived. Dumbledore's self-proclaimed proudest achievement, however, was featuring on a Famous Wizards Chocolate Frog Card.
  _{(old jkrowling.com - Wizard of the Month)}

  
  

  
  


• 
  

  Pottermore

  
  
  
  
  

  • 
    

    Possibly the most infamous World Cup Final of the last few centuries was the Ireland-Bulgaria match of 1994, which took place on Dartmoor, England. During the post-match celebrations of Ireland’s triumph there was an outbreak of unprecedented violence as supporters of Lord Voldemort attacked fellow wizards and captured and tortured local Muggles.
    _{(Pottermore - History of the Quidditch World Cup)}

    
    

  
  

  • 
    

    Cornelius Fudge 1990 - 1996
    
    A career politician overly-fond of the old guard. Persistent denial of the continuing threat of Lord Voldemort ultimately cost him his job.
    Rufus Scrimgeour 1996 - 1997
    
    The third ex-Auror to gain office, Scrimgeour died in office at the hands of Lord Voldemort.
    Pius Thicknesse 1997 - 1998
    
    Omitted from most official records, as he was under the Imperius Curse for his entire term of office, and unconscious of anything that he was doing.
    Kingsley Shacklebolt 1998 - present
    
    Oversaw the capture of Death Eaters and Voldemort supporters following the death of Lord Voldemort. Initially named as ‘caretaker Minister’, Shacklebolt was subsequently elected to the office.
    _{(Pottermore - Ministers of Magic)}

    
    

  
  

  • 
    

    About to turn 34, there are a couple of threads of silver in the famous Auror’s black hair, but he continues to wear the distinctive round glasses that some might say are better suited to a style-deficient twelve-year-old.
    _{(Pottermore - Dumbledore’s Army Reunites at 2014 Quidditch World Cup Final)}

    
    

  
  
  
  

Alternate explanation: The books take place between 1997 and and 2004

Evidence: 

While this isn't the generally accepted answer (for many reasons), there are other (early) canon sources that seem to indicate a different date. 

• The first book was published in 1997 


• Dudley has a PlayStation in Book 4 (they weren't released in Europe until 1995) 
  
  

  
  

  Dudley’s diet isn’t going too well. My aunt found him smuggling doughnuts into his room yesterday. They told him they’d have to cut his pocket money if he keeps doing it, so he got really angry and chucked his PlayStation out of the window. That’s a sort of computer thing you can play games on. Bit stupid really, now he hasn’t even got Mega-Mutilation Part Three to take his mind off things.
  _{(Harry Potter and the Goblet of Fire - Chapter 2)}

  
  

  
  


• The Daily Prophet Newsletters are dated 1998-1999 and are set in the timeframe of book two and three. (Fudge is the Minister, Dumbledore is the Headmaster, etc.) 

It should be reiterated that this way of calculating the dates is contradicted by practically all other canon, and is not the generally accepted answer.

Visual timeline with months/days/years

The first person to do this on a large scale is Steve Vander Ark, creator of The Harry Potter Lexicon. His dating of events is widely accepted, appearing in places ranging from HP wikia to bonus features of the Chamber of Secrets film dvd. His original timeline can be found here.