Significance The somatosensory barrels are a unique feature of the rodent cortex. Each barrel represents a functional unit in which clustered innervation from an individual whisker connects with a ring of cortical neurons. This study reports that when a single transcription factor, LIM homeobox 2, is deleted specifically in the cortex, neither the barrel cores nor the cortical barrel walls are able to form, although a rudimentary functional mapping of the somatosensory innervation does occur. Understanding how barrels form will shed light on how functional neurocircuitry is assembled in its final stages, and this insight may be broadly applicable in the nervous system.