Proper formation of the shape and size of cortical functional areas is essential for complex brain function, including sensory perception and motor control. Our previous work identified the transcription factor Lim domain only 4 (Lmo4), a regulator in calcium-dependent gene transcription, that has unique, region-specific expression in postnatal mouse cortices with high expression anteriorly and posteriorly but very low expression in between. Here we report that Lmo4 expression coincides with the timing of the development of the somatosensory barrel field. Lmo4 cortical deletion causes changes in expression patterns of cortical regional markers and results in rostro-medial shrinkage but not rostral or caudal shift of the somatosensory barrel subfield. Fine regulation of accurate shape of the barrel subfield by Lmo4, as well as Lmo4-mediated calcium-dependent gene expression, is critical for normal brain functions, as Lmo4-deficient mice display impaired sensorimotor performance. Moreover, even though Lmo4 has broad expression in the central nervous system, it plays a subtle role in the development of non-cortical regions. Our results reveal a new mechanism of cortical area formation and normal sensorimotor control that is regulated by genes with region-specific expression in the developing cortex.