This report presents a comprehensive data release exploring the tissue microarchitecture of P7 aged mice using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) combined with machine learning-based segmentations of nuclei. The study includes high-resolution 3D volumes and nucleus segmentations for seven vital tissues - pancreas, liver, kidney, heart, thymus, hippocampus, and skin - from a single mouse. The detailed datasets are openly accessible on OpenOrganelle.Janelia.Org, providing a valuable resource for the scientific community to support further research and collaboration.