Irwin's Farm is a small farm outside the Hub owned by Irwin, which was forcefully overtaken by raiders. The Vault Dweller can only be taken there by Irwin himself, during the Help Irwin quest. Inside Irwin's farmstead are a total of seven moderately equipped raiders, spread around the interior.
If having left the farm, it's impossible to return there, even if not all the raiders are killed.
The Vault Dweller must have a minimum Level of 5 to get to this place.
Prepare well for this fight, you will encounter seven raiders in relatively narrow space.
If accompanied by companions, they tend to rush into the house upon the beginning of combat, only to be surrounded by raiders in no time. To prevent a quick demise of your teammates, go to the west corner of the map and dismiss your non-player character(s). As there is only one entrance to the farmstead, open the door, and position your PC inside the doorframe to block the passage. Initiate combat and your teammates will come to help, despite them being dismissed. You can just re-recruit them after the fight.