The location for this mission is quite hard to find. It is located deep within the woods in southeastern Spencer's Mill. To locate the place, traverse the road North of the Church Home Base and before reaching the very top end, you will notice a marked sign which leads to a small dirt road on the right. This path leads deep into the woods and be careful going into it since there are multiple trees and bushes which can be quite the obstacle.
You will be tasked to defend the house from incoming hordes. Quickly get some supplies and ammo in the supply locker in the first floor then fortify the barricades of the nine windows in the lower floor. Wait until zombies destroy the windows and enter one by one. Simply kill all the zombies that get in, this way you will not get swarmed and overwhelmed.
Towards the end part, a Big 'Un will attack the house, go back to the supply locker and use all the explosives against it. Take the chance to shoot it multiple times if it gets stuck in the window. Another option is to get out of the house and ride your car and keep hitting the big guy with the back of your car while in reverse.
After the onslaught, head to the top floor and kill Eli to clear the mission.