Technologies to visualize whole organs across scales in vivo are essential for our understanding of biology in health and disease. To date, only post-mortem techniques achieve cellular resolution across entire organs. Here, we demonstrate in vivo volumetric ultrasound localization microscopy (ULM). We detail a universal methodological pipeline including dedicated 3D ULM, motion correction and realignment algorithms, as well as post-processing quantification of cerebral blood diameter and flow. We illustrate the power of this approach, by revealing the whole rat brain vasculature at a 14-fold improved resolution of $12 ~mu text{m}$