Pokémon Brilliant Diamond and Shining Pearl have a variety of rarer Pokémon for players to track down on their journey throughout the Sinnoh region. Some are more difficult to find than others, like Porygon, which hides in a specific area. This classic Pokémon is native to only one area of the map, so you might need some help to track it down.
Players can find Porygon in the Trophy Garden after defeating the Elite Four in Pokémon Brilliant Diamond and Shining Pearl. The Trophy Garden is on Route 212, behind the Pokémon Mansion. Porygon isn't the only rare Pokémon that players can find in this area, as the Trophy Garden has plenty of rarer creatures that are great for a trainer looking to bolster their team, including Clefairy, Plusle/Minin, and Mime Jr.
To evolve your newly found Porygon into a Porygon-2, you'll need to track down Up-Grade. Getting this item is tedious in Brilliant Diamond and Shining Pearl, as you'll need to complete the Sinnoh Pokédex and speak to Professor Oak just outside of the Eterna City Gym to gain this item. Head over to Gamepur for a more detailed explanation of earning Up-Grade.
Once you have the Up-Grade, you'll need to trade Porygon while holding this item, so try to find a friend you know will give this special Pokémon back. To evolve it once more into Porygon-Z, you'll need yet another item: The Dubious Disc. Check out the video below for info on how to earn that item.
For an in-depth breakdown of the Trophy Garden, be sure to visit the Bulbapedia Page.
For more on Pokémon Brilliant Diamond and Shining Pearl, be sure to check out our other guides like Best Nature for Heracross in Pokémon Brilliant Diamond and Shining Pearl here on Pro Game Guides.