[Linked Image from i.imgur.com]
Here is how I built this deck, after I built the log cabin.


[Linked Image from i.imgur.com]
I dug holes 16x16 and 12 inches deep. I am down in Dixie and that is the spec for frost heave. In Yankeeland, much deeper.
I filled the holes with concrete. If you are using Sakrete get the stuff in the red bag it is better than the stuff in the yellow bag.
I set 1/2 inch galvanized bolts in the wet concrete. Two days later I bolted the galvanized "chairs" onto the concrete, then attached the posts to the chair.

One mistake I made, and it is a small one. Build little 2x4 frames, 16x16 ID, and set this on top of the hole. Then pour the concrete, this way, the concrete will be 4 inches higher than the surrounding dirt. If the post is at ground level you have to go around every few years and scrape away the dirt and leaves because I don't want
that post under ground.

It is good to have the post bolted to the concrete because if this deck is in your yard, and somebody is backing up late at night and they hit your post, your deck will collapse.