How do I create directory if it doesn't exist to create a file?

To Create

(new FileInfo(filePath)).Directory.Create() Before writing to the file.

....Or, If it exists, then create (else do nothing)

System.IO.FileInfo file = new System.IO.FileInfo(filePath);
file.Directory.Create(); // If the directory already exists, this method does nothing.
System.IO.File.WriteAllText(file.FullName, content);

You can use following code

  DirectoryInfo di = Directory.CreateDirectory(path);

As @hitec said, you have to be sure that you have the right permissions, if you do, you can use this line to ensure the existence of the directory:

Directory.CreateDirectory(Path.GetDirectoryName(filePath))