The corticospinal (CS) tract is essential for voluntary movement. Despite numerous studies, what we know about CS tract organization and development remains limited. In our previous study, we injected retrograde tracers into the 7th segment of cervical spinal cord (C7) in the infant and adult mice and analyzed the number and distribution of the labeled neurons in the cortex. The number decreased during development, whereas the extended areas of the distribution in infants and adults were similar to each other, and the areas in both animals contained secondary motor (M2), primary sensorimotor (M1/S1) and secondary sensory cortices (S2). Many C7-projecting neurons in infant mice survived until adulthood, indicating that the reduction in the number of labeled neurons mainly due to axon branch elimination. Furthermore, morphological and electrophysiological analyses revealed that, in infant mice, at least more than 80% of CS axons made synapses with spinal neurons widely distributed in the C7 gray matter. By contrast, the cortical areas innervating L4 are limited to the conventional hindlimb area, and the cell distribution and density showed little or no change during development. In the present study, to investigate the developmental changes of axonal distribution of CS neurons located in M1/S1, M2 and S2, we injected adeno-associated virus serotype 1 vectors expressing fluorescent proteins (XFPs) of different colors, which were fused with channelrhodopsin-2 (ChR2) into the cortical areas separately at P0. ChR2-XFPs labeled axons clearly without gaps down to their terminals because ChR2 is the transmembrane protein, and the tagged XFPs are located just beneath the plasma membranes of axons. In addition, these neurons can be activated by photostimulation. The mice underwent the viral injections were fixed at P7, P14 and P21. We analyzed the axonal distribution in the C7 and found that the axon terminals derived from M1/S1 and S2 in the spinal cord were differentially distributed. CS axons from S2 were predominantly distributed at the dorsal part of spinal cord, and those from M1/S1 were observed at both dorsal and ventral parts.