These are all the locations of the available companions in fallout 4. some of them require you to do some missions for them before you get the option of asking them to join you. Others will join you right away and some you have to keep playing the main story to get access to them.
00:00 - CODSWORTH
Perk: Robot Sympathy
Effect: +10 damage resistance against robot energy weapons
Bio: A robot with the loyalty of waiting 200 years for your return and spending 10 of those years waxing your atomically stained floor. Codsworth can be found at your own house in Sanctuary Hills.
00:23 - DOGMEAT
Perk: None. But your Attack Dog perk can be used on him and he can be equipped with armor and handkerchiefs. He also starts with maximum affinity level.
Bio: The dog is the second companion you will encounter as you progress through the main story. Shortly after you leave Vault 111 you’ll come across the Red Rocket Truck Stop, you’ll find Dogmeat here.
00:52 - PRESTON GRAVEY
Perk: United We Stand
Effect: when facing three opponents or more, +20% damage and +20% damage resistance
Bio: Early in the game you’ll come across the town of Concord. There’s a quest there called When Freedom Calls. Complete that to unlock Preston as a companion.
01:54 - NICK VALENTINE
Perk: Close to Metal
Effect: one extra guess and 50% faster terminal cooldown while hacking
Bio: Nick Valentine is a detective that you encounter during the main quest line. Complete the quest Unlikely Valentine to unlock this companion.
02:46 - PIPER
Perk: Gift of Gab
Effect: +100% XP bonus for speech challenges and discovering new locations
Bio: This feisty young companion is located in Diamond City. She helps you enter the city during the quest chain, speak to her after the quest objectives to make her a companion.
03:32 - CURIE
Perk: Combat Medic
Effect: heal 100 points if health falls below 10%; can only be used once each day
Bio: Located within Vault 81, Curie is another robotic companion. you have to complete hole in the wall with the vault to make her your companion.
04:34 - PALADIN DANSE
Perk: Know Your Enemy
Effect: +20% damage when fighting Ferals, Super Mutants, and Synths
Bio: A member of the dreaded Brotherhood of Steel. A short distance from Diamond City is the Cambridge Police Station, in Boston. Once you speak with Paladin and join his faction wait for the reinforcements to arrive and complete his missions he will be available as a companion.
05:28 - CAIT
Perk: Trigger Rush
Effect: when health falls below 25%, action points regenerate faster
Bio: Cait is deadly in combat and fantastic with locks. Head to the combat area within Boston and clear out all the Raiders there, Cait will join you soon after.
06:23 - DEACON
Perk: Cloak and Dagger
Effect: +20% sneak attack damage, +20% Stealth Boy duration
Bio:Another companion located off the beaten track. Head to the HQ of the Railroad and check in the Old North Church. He can also help you join a new faction. After you finish the Tradecraft quest he will join you.
07:56 - HANDCOCK
Perk: Isodoped
Effect get criticals 20% faster at 250 rads and up
Bio: Check out Scollay Square inside Goodneighbor for a chance to meet John Hancock. After you finished the recruiting hadcock quest he will become your companion.
08:41 - MACCREADY
Perk: Killshot
Effect: +20% chance of headshots in VATS
Bio: Another seemingly dodgy contact within Goodneighbor. If you pay him 250 bottle caps we will offer his services to you as a companion.
09:53 - STRONG
Perk: Berserk
Effect: +20% melee weapon damage when health falls under 25%
Bio: During the quest Curtain Call there’s a large tower, Trinity Tower, at the top you’ll find Strong locked inside a cell. Release him from his cell and complete the quest to recruit him as a companion.
12:19 - X6-88
Perk: Shield Harmonics
Effect: +20% damange resistance vs. energy
Bio: Continue through the main story until you reach the Institute location. You can’t miss him so just work your way through the quest.