This is my first submission and success without using discussion posts for help. It uses Depth First Search recursion hitting each node. It keeps track of the node's depth as we go and if it surpasses the max depth recorded, it will set depth = to the nodes level.

```
//set our global max depth value
public int depth = 0;
public int maxDepth(TreeNode root) {
if(root == null) return 0;
else depth = 1;
//call Depth First Search with a starting level of 1 - level will keep track of the nodes depth
DFS(root,1);
// return our global depth value
return depth;
}
public void DFS(TreeNode root, int level){
//This shouldn't be hit but just in case we will return if the node is null
if(root == null) return;
//if the nodes depth is > global depth, set global depth = nodes depth
if(level > depth) depth = level;
if(root.left != null){
//Go down the left side of tree, increase the node's level to keep track of what depth it is
DFS(root.left,level+1);
}
//hit the right nodes if they exist, keeping track of node level
if(root.right!= null) DFS(root.right,level+1);
}
```