There's no question that one of the most comical subplots in Parks and Recreation is that of Pawnee's abysmal raccoon infestation; here's the real reason why raccoons flock to the small Indiana town. According to protagonist Leslie Knope, played by the hilarious Amy Poehler, the raccoons have been a part of Pawnee for as long as she has. They're even the reason behind Leslie's birth at rivaling town Eagleton's hospital. Apparently, the Pawnee hospital was overrun with raccoons at the time, and Marlene Griggs-Knope was forced to give birth to Leslie one town over. While the small town faces the biggest problems with raccoons, they also have a possum issue, highlighted in season 2, episode 18, when the possum "Fairway Frank" bites the Mayor's dog.
In Parks and Rec, Leslie Knope's book Pawnee: The Greatest Town in America cites that the raccoon problem started in 1935 because Eagleton used the town as their personal landfill. She states that the scientifically deemed "raccoon blizzard" is caused by the trash pile-up, but they stay because of "Pawnee's hospitality." The pests become somewhat of a mascot for the town. The fictional book cites that raccoons are a popular child's Halloween costume, and a town favorite activity is "Rocky Spotting" in the summer. While this might be a reason as to why the raccoons came, it's not the real reason as to why the infestation grew and stuck around for generations.
The real reason behind Pawnee's raccoon infestation starts and ends with the neighboring town of Eagleton. Unsurprisingly, the town made Pawnee their personal landfill, attracting raccoons and possums to the area. However, the hated town of Eagleton purposely keeps Pawnee infested with the pests. How? By having literally zero trash in their town. In Parks and Rec season 5, episode 8, Leslie gets the chance to tour one of Eagleton's public parks. One of the things she points out is that the park has not a single trash can in sight. She throws her trash on the ground, and an Eagleton employee picks it up immediately, saying, "Thank you for the trash." As well, throughout the merger process of the two governments (a season 6 plotline), Leslie notices that they spend a ridiculous amount of money on putting together programs like the department of "horse dressage." Chances are, the Eagletonian municipal waste department is also grievously over-funded. This means that if the town or townspeople have any trash, it's probably picked up pretty fast. Thus, there's nothing to even attract the raccoons out of Pawnee, simply because they have nothing to eat.
Unfortunately, in Parks and Recreation, the titular town does little to help with the problem despite Leslie Knope's best efforts. The Sweetums factory produces just as much waste as it does unhealthy products, giving the raccoon swarm plenty to scavenge. Adding on to that, Pawnee is full of fast-food chains, once again giving the pests plenty of trash to flock to. Townspeople seem to have complacently accepted the issue; therefore, they don't put too much effort into keeping their town clean. Their pest control department isn't efficiently staffed or run well enough to even begin to tackle the problem. So, just like Pawnee's famous Lil' Sebastian, the raccoon problem becomes a weird mascot that the town blindly welcomes.
As previously stated, the raccoons aren't the only pest problem that the town has. Possums aren't the biggest issue, but Knope's book states that they used to be a bigger obstacle. She even says that townspeople swear they've encountered a raccoon/possum hybrid that has "eight legs and can run 30 miles per hour." Parks and Recreation's town of Pawnee faces this major issue because of Eagleton. However, the hilarious subplot is never resolved in the series, and it seems like the townspeople don't really care that much.