In 1987, James Brennan's dreams of a summer European tour before studying at an Ivy League school in New York City are ruined after his parents have a severe career setback. As a result, James must get a summer job to cover his upcoming expenses at the decrepit local amusement park, Adventureland, where he falls in love with a witty co-worker, Emily Lewin. In that bizarrely shady workplace, the young carnies have unforgettable and painful learning experiences about life, love and trust while James discovers what he truly values.
It's the beginning of the summer 1987 in Pittsburgh. Young adult James Brennan, who is inexperienced in more ways than one including being a virgin, has just graduated from college with a degree in comparative literature. His parents are sending him to Europe for a six week vacation as a graduation present before he heads to New York City to attend Columbia's graduate program in journalism. He is taking the trip and sharing an apartment in NYC with his best friend Eric, James' half of the rent being paid for by his parents. As his parents announce they can no longer financially support him, the trip is definitely off, but his stint at Columbia is placed into jeopardy unless he can make enough money both over the summer and in NYC to pay rent. With no marketable job skills, he takes the only summer job he can get, at a third rate amusement park called Adventureland as one of the many games operators. At Adventureland, James believes he's died and gone to hell until he meets fellow games operator Emily Lewin, to who he is attracted. Not having any real experience with women, James is taken under the wing of the park's good looking maintenance man, married Mike Connell. As James and Em embark on what looks to be a relationship, secrets that Em and Connell are keeping as well as an encounter James has with Lisa P., a fellow parks worker who is the dream girl of every red blooded man in the park, may jeopardize James and Em's relationship. But James' experience at the park that summer may also provide him with a clearer picture of what he really wants and needs in his immediate future.
In the summer of 1987, a college graduate takes a 'nowhere' job at his local amusement park, only to find it's the perfect course to get him prepared for the real world.
- It is the summer of 1987 and James Brennan (Jesse Eisenberg) has just graduated with a comparative literature degree from Oberlin College. He is looking forward to touring Europe for the summer and going to Columbia University for graduate school in journalism when his parents (Wendie Malick and Jack Gilpin) announce they won't be able to help him financially.
James looks for summer jobs, but can only find one, at Adventureland, a local amusement park in his hometown of Pittsburgh, Pennsylvania where his childhood friend Frigo (Matt Bush), who has a habit of punching James in the testicles, works. James is hired immediately by the assistant manager, Bobby (Bill Hader), and is assigned to the games area. He meets some of his co-workers: the dry and sarcastic Joel (Martin Starr), Bobby's wife and manager of Adventureland, Paulette (Kristen Wig), Sue O'Malley (Paige Howard), Mark (Mark Miller), Lisa P. (Margarita Levieva), and the park's repairs technician Mike Connell (Ryan Reynolds), who is a part-time musician and claims to have once jammed with Lou Reed.
James meets another games worker, Emily "Em" Lewin (Kristen Stewart), after she saves him from being stabbed by a disgruntled customer. She later invites him to a party at her house. During the party, Em invites him to join her in the pool. After the party ends, it's revealed that Em has been having an affair with Connell, although he is married. James goes out to a bar for a drink with Em, and while they are talking at the bar, Em is surprised to learn James is still a virgin. Connell arrives at the bar and Em wants to leave, so they go to one of Pittsburgh's three rivers close to one of the city's bridges where James kisses her. The following day, James tells Connell about his strong feelings for Em, which Connell reports to Em. Em later tells James she wants to take it slow.
The next morning, Lisa P. asks James out on a date, but only lets a few people know. After James returns from the date, he learns Em had called to tell him that she regrets having rejected his feelings on their past date. James gives Em some of his marijuana to bake pot cookies to cheer her up. After a pot-induced game-playing streak, Joel is attacked by an angry customer who learns the games are rigged. When Em steps in, the customer pushes her and James defends her by punching him in the balls. The customer's friend starts chasing James who hides in Bobby's office, who then scares the customer off by threatening him with a baseball bat. Em tells James that she doesn't want to lose him.
Joel sees them walking together and decides to quit. James tries to talk him out of it but Joel is angry at James for dating Lisa P. when he already loves Em. James wants to be honest and tells Em about the night he went out with Lisa P. Shocked by his honesty, Em goes to Connell's house that night to end their affair. Prompted by Frigo, the park's mentally challenged parking official tells James he saw Em and Connell doing "push-ups without any pants on" in the back of Connell's car a few weeks earlier. James goes to Connell's house and sees Em leaving, having just broken up with Connell. When James confronts Em, she is so shocked to see him there that she becomes tongue-tied and does not explain; James becomes angered by the assumed betrayal, and leaves after Em calls herself an "idiot". Later, James tells Lisa P. about the affair, but asks her not to tell anyone.
Lisa P. tells her friend Kelly, and soon everybody in the park has found out and Em quits. James is heartbroken and drunkenly crashes his dad's car into a tree and passes out. The next morning, his mother wakes him up and tells him that he has to pay to fix all the damage. After getting his last paycheck, Connell tells James that he has not spoken to Em since she quit. James doesn't have enough money to go to graduate school, but heads for New York anyway. In New York City, James waits outside Em's apartment. She's surprised to see James waiting for her and is reluctant to talk to him, feeling she has ruined everything between them. James tells her that he sees her in a different way than she sees herself, that he sees the girl who saved him from getting knifed, the girl who stood up for Joel, the girl who introduced him to psychotropic cookies, and the girl who doesn't make apologies for herself. Touched, Em brings James up to her apartment. Once there, James gets out of his wet clothes, and finds she still has an Adventureland shirt. They kiss and begin to take their clothes off as the film ends, and James presumably finally loses his virginity to Em.