The Nancy Drew Files, spin-off River Heights, and spin-off crossovers with The Hardy Boys Casefiles explicitly places River Heights in Illinois. #10 Buried Secrets involves Nancy looking into a 30-year-old cold case where the victim, John Harrington, at the time of his death was running for governor of Illinois. #4 Smile and Say Murder has Nancy commuting via train into Chicago.

The later Nancy Drew Mystery Stories (published during the late 90s and early 2000s) also places River Heights in Illinois. This is explicitly stated in The Missing Horse Mystery, which deals with the Dressage Grand Prix and has Nancy at one point crossing the state border into Iowa.

As far as the original yellow hardbacks go... I think that varied by ghostwriter, but for the most part, River Heights was implied to be in the Midwest.

The Her Interactive PC games series, from what we're shown of Nancy's travel itinerary at the start of some games, shows her leaving from River Heights that's definitely in the Midwest area, most likely Illinois.

Why do people largely assume Nancy and River Heights are located in the Midwest, specifically Illinois? Because it's outright text in various continuities.

Can anyone answer the same question for The Hardy Boys on where the hell is Bayport? Is this explicitly mentioned across various Hardy Boys media the way it is Nancy Drew? The Casefiles universe, maybe?

Chic Boutique’s Chic Week door buster begins at their storefront in River Heights.

yeah girl

this happens you like once a week - atp nancy is never driving without also being followed or at least she is following someone

Nancy Cracks The Case

Nancy looked up as Sheriff McCann’s vehicle screeched into the clearing. The policeman leapt out his car, its blue lights flashing, an anxious expression on his face. He pulled up short when he saw the scene ahead of him, illuminated by his headlights. “Nancy!” he exclaimed. “I got a message from your friends that you had figured out who the blackmailer was and that you were going to confront him in River Heights woods. They were scared you would get yourself kidnapped!”

Nancy looked up from tying up a sullen but defeated looking Joe Korner. “Well it certainly happens, sheriff!” the redhaired detective smiled wryly. “But this time I was able to get the drop on the bad guy for a change!” McCann smiled too, anxiety slowly being replaced by relief on the experienced sheriff’s grizzled features. “Who is he, Miss Drew?” he asked. Nancy finished tightening Korner’s bonds and, breathing hard from the effort, replied: “This is Mr Joe Korner - poet, artist and blackmailer. I have a full recorded confession from him on my phone from when he was gloating at me, thinking he had me trapped. He’s all yours, sheriff!” McCann stepped forward to take hold of the despondent prisoner. “I’ll get you for this, Nancy Drew!” Korner muttered as the sheriff led him away. The girl sleuth beamed in satisfaction. “That’s what they all say, sir!” she replied.

Nancy’s AI Adventure, Part 6

Nancy put a protective arm around DuPont’s tensed shoulders. “Don’t worry, monsieur,” she hissed in the restauranteur’s ear, “no one will harm you while you are my prisoner!” Marcel grunted but whether from gratitude or resentment she couldn’t tell. The man had said two of his people were also working with the cartel. “Your, er, associates, monsieur,” Nancy continued, “is one of them a woman?” Marcel snorted. “A woman?” he repeated derisively. “Of course not!” But then stopped, realising how incongruous his sexism was when he had just been captured by a woman. Nancy was used to misogyny in her line and took no heed. Instead, she braced, ready for action once more as the female form came into focus.

Then her face widened into a broad smile. “George!” she exclaimed as she recognised her friend. “Oh it’s good to see you!” She ran forward to embrace the dark-haired girl, laughing with delight and relief. “We had tried everywhere else, so we figured you had to be here in the restaurant cellar!” George replied, hugging Nancy. “This is a very fishy operation,” she went on, “and I don’t mean the menu!” Nancy nodded. “I know, George.” she smiled. “Monsieur Dupont here has made a full confession!” George looked over at Nancy’s bound captive. “Honestly, Nance, you are amazing!” she laughed.

“We need to get him to the sheriff so he can tell him everything he told me.” Nancy told her friend earnestly. “Dupont has enough on the drugs ring to sink it entirely in River Heights!” George nodded. “I don’t think he is a one man band though, Nance.” she replied. “Bess is in the restaurant now, trying to see if she can winkle out a confession too.” Nancy walked over to the surly looking Dupont. “Maybe if they see their boss is caught, it will encourage his accomplices to surrender too.” she suggested. Dupont just glared at her. George joined Nancy and together they walked the glowering Dupont down the cellar corridor and towards the stairs leading to the restaurant. “Ready to meet your public, monsieur?” Nancy asked her prisoner ironically.

To be continued.