Easter eggs

Spiffo enjoying the bloodshed in Terraria.

During your time exploring Knox Country, various Easter eggs can be found throughout the area, referencing other games, media, developers etc. Many of these references are in the form of business names, graffiti, items, etc.

Pop-culture

Goodman Legal Services in Louisville is a reference to Saul Goodman, a character in TV Series Breaking Bad and Better Call Saul.

Romero Center for the Performing Arts is a theater in Louisville. The theater's name is a reference to film director George A. Romero. Romero invented the modern zombie with his debut film Night of the Living Dead.
The Crossroads Mall in Valley Station is a reference to the mall of the same name in the film Dawn of the Dead (2004).
The challenge mode 'A Really CD DA' is a reference to the survival game, Cataclysm: Dark Days Ahead.
Goodman Legal Services is a law firm in Louisville, the name is a reference to Saul Goodman, a lawyer in the TV series Breaking Bad and the spin-off series Better Call Saul.
A-1 Laundry are a chain of laundromats that are located in Louisville. The name is a reference to A1A Car Wash, a fictional car wash in Breaking Bad.
It can be possible to encounter a zombie wearing a Hockey Mask and with a Machete on their back. This is a reference to the immortal slasher Jason Voorhees from the Friday the 13th film franchise.
The Waites Motel in Muldraugh, is likely a reference to the Bates Motel from the slasher film, Psycho.
Bateman Office Building in Downtown Louisville is likely a reference to Patrick Bateman, villain protagonist of the 'American Psycho' novel and film adaptation.
Back To The Nurture Chiropractic Services is a chain of chiropractic offices with locations in Louisville and Riverside. The business name is likely a reference to the Back to the Future film trilogy.
Deep in the woods outside of Muldraugh and Rosewood, a message made out of dirt paths can be found. The message is a love heart with the name Brian. This is a reference to Brian Hicks, creative director behind the zombie survival game, DayZ.
A CD called 'Raps for Christ' is likely a reference to a christian hip hop song and internet meme known as Rappin' for Jesus.

The Indie Stone

Some of the graffiti in Knox Country references various developers.

A construction site in Muldraugh is owned by T.I.S. Construction, referencing The Indie Stone, the developer studio behind Project Zomboid.
Spiffo, the game's adorable mascot was a character from PAWS, an unreleased fighting game that Indie Stone were previously working on.
In several areas of Knox Country, you can find "NasKo" spray-painted on a wall, this is a reference to the Community Manager, NasKo.
Some areas also have "RingoD" spray-painted on the wall. The graffiti is referencing former modder, turned developer, Paul Ring.
Enigma Books is a chain of book stores with locations in West Point and Riverside, referencing the Support & Operations Manager, EnigmaGrey.
The hardware store chain Zac's Hardware in Louisville, refers to developer Zac Congo.
A cafe in Louisville, Cafe d'Eris is a reference to Eris, a former modder, turned developer.
The Blue Fox, a restauraunt in Louisville, references developer Fox Chaotica.
One of the Lunchbox variants has the face of Will Porter surrounded by love hearts. Porter is one of the game's writers.
A.A.Ron Hunting Supply is also a reference to Will's son. The business name is also likely a reference to the comedy duo Key & Peele's substitute teacher sketch.
A rare variant of the T-shirt has the face of one of the developers, Romain Dron.
R. Johnson Office Building in Louisville, references Robert Johnson/RJ, an alias used by Dron.
Romuald Dron Memorial Park was dedicated to the brother of RJ, who has sadly passed away. The park is located in Louisville.
A nightclub in Louisville, Beever's references Zach Beever, one of the composers behind much of the soundtrack.
Aitor Wire Company, a factory in Louisville, references developer Aitor Garca de la Cruz.
A clothing store in Louisville, Yuri Design, is named after developer Yuri Yakovlev.
An abandoned factory town near Riverside has "Tanglewood" graffitied on one of the houses, referring to Tanglewood Games, a studio assisting with development.
Andrei and Son Hand-Crafted Wallets is a factory in Louisville, named after developer Andrei Topilin.
The clothing store Sasha Sashay in Louisivlle, is a reference to the Lead QA Tester, Pandorea.

Community

Various members of the community are referenced in the game, such as Twiggy's in West Point, a bar named after former Youtuber and streamer "sirtwiggy"

Twiggy's is a bar located in West Point, the bar is named after sirtwiggy, former Project Zomboid YouTuber and streamer. Twiggy is also one of the callers on KnoxTalk Radio.
KPK Consulting Business Investments in Louisville, references KPKPlays, a friend of TIS.
Hair O Genesis is a chain of barber shops that have several locations in Knox Country, the chain is named after Ontogenesis, a friend of TIS.
A car dealership Nolan's Used Cars, located in Dixie Mobile Park, references nolanritchie, a modder behind several popular mods, one of which being the Driving Cars Mod.
In the woods outside of Muldraugh, you can find Ben's Cabin, the name is referencing a forum user known as haze1434 and it being their base right before the birth of his child. Haze had to leave to go to the hospital because his wife was about to give birth. Their child was named Ben and the cabin was named after them as a way of commemorating this event.
The in-game show Moderators, is a reference to an actual event, when someone on the moderation team tried to ban a user from the forums, but accidentally made them an admin instead. Whoops!

Miscellaneous

The Art Gallery of Louisville contains various references to real life artwork. Various paintings from Vincent van Gogh, the Statue of David, etc.
Sometimes you can find houses with containers filled to the brim with Toilet Paper. This is a reference to global supply shortages during the COVID-19 pandemic, with toilet paper being one of the main items suffering shortages due to panic buying.
A window shop in Louisville named Window (business) is a reference to Microsoft Windows, a series of operating systems developed by Microsoft.

Project Zomboid References

Sandbox game, Minecraft references Zomboid in the main menu. Occasionally there's a splash text saying "Also try Project Zomboid!"
Survival game, NEO Scavenger also occasionally references Zomboid in it's main menu.
Project Zomboid's mascot Spiffo, can be found in the form of a rare plush item in 2D sandbox game, Terraria. The plush acts as a pet summon item, allowing you to summon Spiffo to join you on your adventures.