Hogsmeade is one of the largest wizard-only villages in Europe. Hogwarts students commonly visit it during their free time, but a permission slip signed by a legal parent or guardian is required for admission into Hogsmeade. Visits to Hogsmeade usually occur around the time of holidays, such as Halloween or sometime in winter.
The villagers of Hogsmeade thought the Shrieking Shack was haunted due to frequent noises coming from the building. The noises they heard were actually Remus Lupin transforming into a werewolf. Lupin, James Potter, Sirius Black, and Peter Pettigrew would all go together as young students to the Shrieking Shack to allow Lupin's transformation take place. From there, they would each turn into their Animagus and traverse freely.
 Harry Potter and the Prisoner of Azkaban
Third year students are the minimal years who are permitted into Hogsmeade. This was the first year being given the opportunity to visit the large village for Harry Potter, Ron Weasley, and Hermione Granger. They were given the slips needed to give to their parents for admission before their third school year had begun. Hermione and Ron returned their slips signed, but Vernon Dursley refused to sign for Harry after the incident with him accidentally blowing up his aunt. Harry asked hopefully if Professor McGonagall could sign the slip for him, but she replied that only legal guardians may sign it.
When the first time of the year to visit Hogsmeade came around, Harry was left behind in the Hogwarts castle. With the help of the Weasley twins, who happily give him the Marauder's Map, Harry sneaks out of the castle through a hidden exit while under his invisibility cloak. He meets up with Ron and Hermione at Honeydukes, a candy shop.
Toward the end of the year, Sirius, as Harry's appointed godfather, signs Harry's permission slip.
 Harry Potter and the Goblet of Fire
Visits into Hogsmeade were canceled due to the year-round Triwizard Tournament in Harry's fourth year at Hogwarts.
 Harry Potter and the Order of Phoenix
Harry's fifth year was the first year in which he could legally enter Hogsmeade. The Hog's Head in Hogsmeade was where Hermione, Ron, and Harry recruited members for Dumbledore's Army. The trio brought food and drinks to Sirius in a quaint cave near Hogsmeade while he was in hiding. During one visit to Hogsmeade, Harry and Cho went on a date at Madam Puddifoot's Tea Shop, where many couples go. There, Cho yelled at Harry for being too concerned about accompanying Hermione at The Three Broomsticks. Many visits to Hogsmeade occurred during this year.
Related ThreadsFaeries in hogsmeade - last post by @ Jun 7, 2004
Getting to Hogsmeade - last post by @ Jun 6, 2004