Background: Glucocorticoids (GCs) are key regulators of hematopoiesis, but the effects of chronically elevated endogenous GC levels on hematopoietic stem cell (HSC) function and immune cell development remain poorly understood. Methods: We used a mouse model with adrenocortical cell-specific deletion of hypoxia-inducible factor-1 alpha (HIF1α; P2H1^Ad.Cortex), which results in sustained and systemic elevation of GC. Hematopoietic stem and progenitor cell (HSPC) populations were analyzed phenotypically and functionally. Transplantation assays assessed the regenerative capacity of HSCs. To determine the role of glucocorticoid receptor (GR) signaling, bone marrow from GR-deficient or wild-type donors was transplanted into P2H1^Ad.Cortex or wild-type (WT) recipients. Results: Chronic GC exposure in P2H1^Ad.Cortex mice resulted in HSPC expansion and promoted HSC quiescence and metabolic restraint. Functionally, these HSCs showed enhanced regenerative capacity with superior donor chimerism upon transplantation. There was a marked increase in myeloid progenitors and their progeny, including monocytes and granulocytes. In contrast, B-cell development was significantly impaired, with a developmental block at the pre-pro-B-cell stage. Transplantation studies confirmed that these effects were dependent on GR signaling. Conclusions: Our study reveals a critical role for chronic GC–GR signaling in modulating HSC function, promoting myeloid output, and impairing B-cell development. The P2H1^Ad.Cortex mouse model provides a valuable system to study the hematopoietic consequences of prolonged endogenous glucocorticoid exposure and may aid in understanding the hematologic complications of chronic GC therapy.