Progress in defining the proteome of the developing human brain has lagged behind our understanding of the adult human brain, primarily due to challenges in tissue acquisition and in preservation of anatomical structure during experimental processing. Upon receipt of a single, exceptionally well-preserved 20 post-conception week human brain hemisphere, we conducted fine dissections of 18 anatomically distinct brain regions, including the pia mater. These samples underwent in-depth analysis of both the total and post-translationally modified proteomes, with the aim of creating a reference resource for investigators studying this critical stage of neurodevelopment. Here, we present an overview of the resulting dataset, compare the proteomic profiles across regions, and highlight examples of variable post-translational modifications within individual proteins to guide data interpretation. As expected, unmodified protein profiles reveal substantial differences across brain regions. For instance, pia mater and thalamus are enriched for proteins involved in transcription and chromatin organization, consistent with a higher proportion of dividing cells in these areas at this developmental stage. In contrast, the cortical proteome reflects active synaptogenesis and cytoskeletal remodelling. While inter-regional differences in phosphorylated and acetylated peptides largely mirror those observed in the unmodified proteome with respect to gene ontology categories, the glycosylated peptidome of the pia mater is markedly distinct. This divergence is driven by the secretion of extra-cellular matrix proteins and the region’s intimate association with basement membrane of the pia. Finally, by integrating our proteomic data with publicly available single- nucleus RNA sequencing datasets from the same developmental stage, we identify high-confidence ligand receptor pairs (e.g., L1CAM:CD9,CNTN4:PTPRG, LGALS1:ITGB1) likely involved in thalamocortical signalling.