Danville is a major city in the Tri-State Area. A geographic anomaly, Danville is near the ocean, yet it is within a short driving distance to Mount Rushmore. It has a large suburban area and is surrounded by forest. The population of Danville is 241,000 as seen on a sign at the city limits. 
- Danville Locations: Downtown
- Danville Locations: Suburbs
- Danville Locations: Geographical Points of Interest
10 years in the future
"Act Your Age" shows a version of future Danville 10 years in the future. Danville looks more or less the same as it did in the present times.
20 years in the future
Two possible futures of Danville are known to exist: a good future based on the current timeline where Candace has come to appreciate her brothers, and a bad future where Candace succeeds in busting her brothers when they build the rollercoaster, which leads to Heinz Doofenshmirtz becoming Emperor.
- Main article: Danville (good future)
Danville in the Good Future is shown when Phineas and Ferb travel 20 years into the future in order to get a machine that can fuse wood and metal. 
New look of Danville
In the future, Danville becomes more technological, having self-opening doors, and a device that can merge metal and wood together. Most things are also digital, such as a digital tree. The Museum also added a new wing, which is, literally, just a wing at the top of the roof.
- Candace Flynn - Presumed to have married, most likely Jeremy. Has three children named Xavier, Fred and Amanda.
- Linda – Still running the Antique Shop, presumably with husband Lawrence.
- Heinz - Appears to still be trying to be evil, but is still being foiled by Perry.
- Isabella - Mentioned by Amanda as "Aunt Isabella", suggesting she marries Phineas or Ferb.
- Phineas - Mentioned by Linda as being in Switzerland to receive an award.
- Ferb - Mentioned by Linda as being at Camp David.
- Stacy - Mentioned by Candace as being the president of Uruguay.
- Lawrence Fletcher - Unknown if he's dead or alive.
The Bad Future occurs when the Candace from the Good Future comes back to the day of the rollercoaster and drags her mother out of the supermarket to witness the coaster. The helicopter that Agent P is about to secure a grappling hook to is diverted to rescue the boys. This allows the tinfoil ball to crash into Agent P atop the Doofenshmirtz Evil Incorporated building, while Heinz fell onto a nearby ledge and survives. During the period Agent P is incapacitated, Heinz begins his rise to Emperor.
In this future, the Tri-State Area is morphed into a dystopian society ruled by Doofenshmirtz, with severe ecological damage caused by extensive industrialization. Everyone here is called Joe, so that Heinz can boast that he always remembers everyone's name. Lab coats are required clothing.
Most of the people in this future are named Joe, with a few exceptions:
- Heinz – Is the ruler of this future, because of what future Candace did 20 years ago - busting Phineas and Ferb.
- Perry – Is still in the O.W.C.A., but his lair is in ruins, and because of taking an oath is unable to stop Doofenshmirtz. Based on the conversations, the OWCA appears to still try to stop their ruler, but the oath makes it really hard. Apparently all Doofenshmirtz has to do is tell them not to do something.
- Carl - Carl is seen still working in the O.W.C.A., now as an adult.
- Major Monogram – Is still one of the heads of The O.W.C.A., but is very old.
- The city of Danville was named after creator Dan Povenmire. 
- The population of Danville is 241,000 as seen on a sign at the city limits. 
- According to series co-creator Dan Povenmire:
- "Danville is not in any specific state, it is wherever it needs to be for any episode. It is a short driving distance from the ocean and Mount Rushmore so it doesn't really exist geographically. Much like Springfield on The Simpsons there are many many states with a Danville in them so any one of them can claim it." 
- There are places named Danville located in Alabama, Arkansas, California (Town of Danville), Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Missouri, Maine, Ohio, Oregon, New Hampshire, New Jersey, New York, Pennsylvania, Vermont, Virginia, Washington state, and West Virginia. Also, there are other Danvilles in Canada, Ireland, and South Africa.
- In the episode "Phineas and Ferb Summer Belongs to You!", Phineas says they have 40 hours of daylight. They depart Danville, westbound, early Saturday morning shortly after 5:00 AM. This would place their observed sundown after 9:00 PM the next evening, Sunday. This suggests that Danville lies far north and west in its timezone, like Seattle, Washington. There have been many references to Seattle in the show.
- The city of Danville could also be in Indiana because 46231 is a ZIP code near Indianapolis, IN - which is adjacent to Danville. 46231 is the Fireside Troop number for Isabella's troop.
- The city of Danville could be in New York because in the online game, Hoverboard Tour, the Doofenshmirtz Evil inc. building is there.
- A possible location for Danville might be Illinois. In "Dude, We're Getting the Band Back Together" Danny sings in "History of Rock" that "When I was a boy, down in South Illinois..." Which hints that Danville may perhaps be Danville, IL. It's within a day's drive of Mount Rushmore (although it's 17 hours according to Google Maps), it doesn't have an ocean, but it does have a very large lake. There was a reference in "The Blues Brothers" to the area surrounding Chicago as the "tri-state area," and Interstate 294 connecting Wisconsin, Illinois, and Indiana is known as the "Tri-State Tollway." Also Illinois, Iowa, and Missouri are known as the Tri-States.
- Danville could also be in Wisconsin, possibly around the Milwaukee area, as it is not near and ocean, but is near a very large lake, and is connected to a highway known as the Tri-State tollway. The city of Milwaukee is small enough with around 600,000 people, compared to some of the more major cities. There is an unincorporated community in Wisconsin named Danville, close to the border between Dodge and Jefferson Counties. It is also within a day's drive of Mount Rushmore.
- Danville could be in Minnesota or northern Michigan as they border large lakes and are both close to Mount Rushmore. Also, there is a Minnesota-Michigan-Ontario tripoint in Lake Surperior. However, it can't be in Wisconsin because Jeremy's family is from there. Ontario can't be the location as Danville is in the United States.  
- Danville could be in Florida because Atlantis is said to be in the Bermuda Triangle and they found it. Also a moat could be in Florida and there are small mountain ranges and dry spots. In the episode where Perry is a banana trucker there is a song that says he is going to Alabama and this is right next to Florida. The Lake Nose Monster could be in Lake Okeechobee and could be a huge alligator.
- Another reason that Danville is likely in the northern U.S. is that Jeremy's grandmother Hildegarde once belonged to the "Saskatoon Slashers."  Saskatoon, Canada is about 150 miles north of North Dakota, in the province of Saskatchewan. It follows that a roller derby team wouldn't go too far to compete, even for a championship. However, it is probably too far from Danville, Canada (which is over a thousand miles away in Quebec). Also, Escanaba and Montreal can both be seen from Phineas and Ferb's rock climbing wall, suggesting Danville may be located in Michigan. 
- As of "Let's All Dance Until We're Sick" and "Phineas and Ferb Christmas Vacation!," the location of Danville has been narrowed down to US locations east of the Mississippi River. The broadcast station in Danville has a callsign of WJOP, with the "W" suggesting its eastern location.
- During the end credits of "Hail Doofania!", as Dr. Doofenshmirtz sings the line "And it's floating on an inner tube," he shows a map of the San Francisco Bay Area and highlights San Francisco. The Danville in California is in the Bay Area.
- The Museum of Natural History is an actual place, located in New York. This may mean Danville is near New York, but this can also mean that they were visiting a fictional museum.
- Danville is surrounded by the MOAT, a network of rivers. Manhattan in New York City is surrounded by rivers.
- Danville could be in South Dakota because they once visited Mount Rushmore. Others also might suggest that Danville could be located in Colorado because there's a sight of the Danville Canyon which resembles the "Grand Canyon". Additionally when Doofenshmirtz holds up a magnifying glass over the Tri-State Area, he holds it over the area around Colorado. 
- In Phineas and Ferb The Movie: Across the 2nd Dimension, the 2nd dimension Doofenshmirtz said "Let's just say it's between 3:30 and 4 Eastern Standard Time," meaning Danville is on the east coast.
- In the past, there was once a battle of Danville. 
- It is also plausible that Danville is in Iowa, since their Danville is located very close to a tri-state area.
- Danville could also possibly be near Salt Lake City, because it is within a day's drive to Mount Rushmore, and while not near the ocean, it is near the Great Salt Lake, which has salt water just as the ocean does. It is also close to the Utah-Wyoming-Colorado Tri-State Area.
- It has to be a city with many people and near the beach and kind of touristic.
- According to "Just Desserts"; Danville could be in Nebraska.
- Based on the plane that was hit by Doofenshmirtz's 90-Degree-Turn-Inator in "One Good Turn" changing its destination to Alabama from New York, it can be assumed that Danville is north of Alabama and west of New York.
- As seen in the Milo Murphy's Law episode "Worked Day", Vinnie Dakota and Balthazar Cavendish use a Danville map, revealing that the show takes place in Danville in the same universe as Phineas and Ferb.
- Many of Danville's locations in Phineas and Ferb have been slightly altered and modified in Milo Murphy's Law while generally remaining the same in structure and placement, including the Subway entrance from "Bowl-R-Ama Drama" and the Danville Opera House.
- Danville could be in Virginia. It was confirmed by Dan Povenmire that the Flynn-Fletchers' house address is 2308 Maple Drive. There is a 2308 Maple Drive in Danville, Virginia.
|Doofenshmirtz Evil Incorporated | Googolplex Mall | Huge-O-Records | Little Duffer's | Superduper Mega Superstore|
|Har D Har Toy Store | Mr. Slushy Burger | Mr. Slushy Dawg | Blueprint Heaven|
|Flynn-Fletcher house | Doofenshmirtz Evil Incorporated|
|Swamp Oil 500|