Portal 2 on Steam adds split-screen to co-op mode, Big Picture support - Polygon
Split Screen: Make your own fun
Portal 2 PC Split-Screen Co-Op
Portal 2 Splitscreen and Online Co-Op Detailed.
Portal Companion Collection for Nintendo Switch - Nintendo Official Site
Uhh wtf? What's happening here? (Portal Reloaded coop in split screen, as I can't find ppl. btw it's so damn confusing, and I've played the whole singleplayer campaign...) : r/Portal
Portal 2 PC Splitscreen CO-OP Fun Gameplay - YouTube
Save 90% on Portal 2 on Steam
Portal 2 PC adds splitscreen co-op - GameSpot
Portal 2: Co-op Splitscreen Multiplayer Gameplay Walkthrough - GOOD GAME | Part 2 - YouTube
Steam Community :: Guide :: How to play Local Co-op with Controller + Keyboard