Van der Waals materials exhibit a variety of states that can be switched with low power at low temperatures, offering a viable cryogenic ‘flash memory’ required for the classical control electronics for solid-state quantum information processing. In 1T-TaS2, a non-volatile metallic ‘hidden’ state can be induced from an insulating equilibrium charge-density wave ground state using either optical or electrical pulses. Given that conventional memristors form localized, filamentary channels which support the current, a key question for design concerns the geometry of the conduction region in highly energy-efficient 1T-TaS2 devices. Here, we report in operando micro-beam X-ray diffraction, fluorescence, and concurrent transport measurements, allowing us to spatially image the non-thermal hidden state induced by electrical switching of 1T-TaS2. The results reveal a long-range ordered switching region that extends well below the electrodes, implying that the self-organized, collective growth of the hidden phase is driven by charge rearrangement and concomitant lattice strain. Our combination of techniques showcases the potential of non-destructive, three-dimensional X-ray imaging to study bulk switching in microscopic detail, exemplified here by electrical control of the charge-density wave state of a van der Waals material.