From Nookipedia, the Animal Crossing wiki
In Animal Crossing
In Animal Crossing, fireworks can be seen in the river on the 4th July, which coincides with American Independence Day. They also appear during New Year's Eve, to celebrate the end of the year and the beginning of a new year.
In Animal Crossing: Wild World
In Animal Crossing: Wild World, the fireworks for Independence Day were removed, and a new event which happens every Saturday in August at 7:00pm takes its place called the Fireworks Show. During the Fireworks Show, Tortimer will be outside the Town Hall. The player can talk to him to receive either a Sparkler or a Roman Candle. Tortimer will usually only allow the player to receive two of each item a night, but if they pester him long enough, he might give out more. Both Sparklers and Roman Candles are equippable items. Once equipped, the player can use one of these items. Both objects shoot out sparks. Tortimer may also give the player a fortune for the night, which appears in a mail slot in their inventory. Fireworks also appear during the New Year's Eve celebrations.
In Animal Crossing: City Folk
In Animal Crossing: New Leaf
In Animal Crossing: New Leaf, the Fireworks Show was significantly upgraded. However, the shows continue to be held every Sunday in August. Isabelle will host the festivities in the Event Plaza, handing out one of the four bopper items (Bulb, Flower, Heart, or Star) and allowing the player to submit a custom design to be used as a firework design during the show. Redd will also open a Cookie Stand in the plaza, where he will sell Redd's Cookies for 500 Bells. These can be eaten, and can contain either a prize ticket (which can be redeemed for an exclusive item) or a Dud Ticket (which are only rewarded with a Sparkler or Roman Candle). Fountain Fireworks are also a new addition to the Fireworks Show. In addition, villagers will clap as they watch fireworks in the sky.
Prize Ticket Prizes