Non‐technical summary  It is not well understood how all of the connections among neurons required for the brain to process information are established during development. It has recently become apparent that waves of spontaneous electrical activity spread across large groups of neurons during early brain development and that these waves of activity are crucial for correct development of brain circuitry. In this paper, we show that waves of spontaneous electrical activity propagate across the mouse cerebral cortex, beginning on the day before birth and continuing through the first 12 postnatal days. These waves are initiated at specific locations in the cortex, which do not change during the period of wave generation. Identity of the neurons that initiate the waves, however, does change during this time. This work indicates that even though spontaneous electrical activity occurs during a short contiguous period of development, the mechanisms underlying that activity change.