Theobald and Jacob arrived in Philadelphia, Pennsylvania on 11 Sep 1728 aboard the ship "James Goodwill," James Crockett, master. The "James Goodwill" sailed from Rotterdam, Holland to Deal, England. From there, on 15 Jun 1728, it left for America.

There is some question about the geographic origin of the Mechling brothers. They were listed among the Palatines aboard the ship. One great-great-grandson listed their home as being in Rheinfels, Bavaria. I don't find a reference to a town of that name in modern Germany—however, this might refer to the area around Castle Rheinfels, situated in the northern portion of the Lower Palatinate, near the current town of St. Goar between Mainz and Koblenz. This is now part of the state of Rhineland-Pfalz, but was controlled by the ruler of Bavaria at various times during that period in history.

The term "palatine" was not always applied strictly. The ships carrying them to the New World often simply listed all German-speaking Protestants as "palatines". This leaves room for two other theories about their place of origin.

The Mechling families from the area of Hoerdt, just north of Strasbourg in the Alsace province of France, have established the Mechling surname in the area as early as 1492. Like the Lower Palatinate, this area was also hit extremely hard by the German/French struggles for control, and large numbers of emigrants travelled down the Rhine to Rotterdam to seek a new home.

Finally, a third possibility lies in northeastern Germany. The Mechling brothers were Lutheran, which was more common in the northeast than the southwest of Germany. Further, Theobald's oldest son, Dewalt, named two of his properties in Westmoreland Co., Pennsylvania "Mechlinburg" and "Strelitz." These are place names in what is now the state of Mecklenburg-West Pomerania, in the extreme northeast of Germany.