If the county designated for that purpose in the summons and complaint is not the proper one, the action may, however, be tried therein, unless the defendant, before the time of answering expires, demands in writing that the trial be conducted in the proper county, and the place of trial is thereupon changed by consent of parties, or by order of the court.
The court may change the place of trial in the following cases:
(1) When the county designated for that purpose is not the proper one.
(2) When the convenience of witnesses and the ends of justice would be promoted by the change.
(3) When the judge has, at any time, been interested as party or counsel.
(4) When motion is made by the plaintiff and the action is for divorce and the defendant has not been personally served with summons.