Amity Park is the hometown of Danny and most of his friends. The town derives its name from the actual town, Amityville, where the story The Amityville Horror takes place.
Amity Park is used in Nickelodeon's Show Danny Phantom. It is depicted as a moderately large city--mainly an urban city, reminiscent of Chicago, San Francisco, and Philadelphia. The City has several downtown areas with modern skyscrapers. Amity Park is home to an Observatory, City Hall, Major Research Lab, Museum, School System, Fire and Police Departments, Restaurants and a Shopping Mall.
Despite knowing this off hand, in the show Amity Park's exact location isn't specified, but several clues hint towards a possible location in the central United States. In the TV movie "Reality Trip", Danny Phantom and his friends travel cross-country to locate a trio of magical "Reality Gems", one of them is located in Florida and California and Navada respectively. Danny first travels to Florida to find the first gem, which is closer to the central U.S. than California or Nevada. This is also supported by two other episodes in the series. In Memory Blank, Lancer points his stick towards the Louisiana area of the United States. Also in Urban Jungle, the roots spread from the Great Lakes region of the United States to the rest of the world--this hints that, possibly, the Lake Eerie ("Girls Night Out", "Claw of the Wild") actually replaces the real Lake Erie.
In the episode Fanning the Flames, Mr. Lancer mentioned the Northwestern Standardized Testing. Now while this could mean that Amity Park is located in Northern California, Oregon or Washington, it could also refer to Northwestern University which is in Evanston, Illinois. Many episodes did suggest Amity Park having beaches and even palm trees, suggesting that Amity Park was on the West Coast. Although, the body of water next to Amity Park could have very well been Lake Michigan. In the episode "Double Cross my Heart", Elliot mentions being from Michigan, revealing that Amity Park is not in Michigan.
Another sign that Amity Park is located in the central United States is the episode Bitter Reunions, where Danny & his family accompany his father, Jack Fenton, to Wisconsin for his 20th College Reunion.
Amity Park's name is a reference to the real world town of Amityville, where the paranormal novel/movie The Amityville Horror and the allegedly true story it is based on took place.
David Kaufman, voice of Danny Fenton, approximates Amity Park to be somewhere in Minnesota