Grandjean Family History

French: from French grand ‘tall’, ‘large’ + Jean (French equivalent of John), hence a nickname (‘Big John’), or a distinguishing name for the older of two bearers of the same personal name. As a nickname it may have been applied in a literal or ironical sense, or as a means of distinguishing between members of the same family with a common personal name. This is a common name in Switzerland, and in some instances may have been brought to the U.S. from there.

Source: Dictionary of American Family Names ©2013, Oxford University Press