The innate immune response is the host’s first line of defense, promptly activated upon pathogen invasion. Its precise and rapid activation relies on innate immune cells (IICs). Upon recognizing danger signals postinfection or injury, they release various innate immune effectors to eliminate invading pathogens or damaged cells, thus supporting the host’s immune homeostasis. Epigenetic modifications, by shaping chromatin structures, orchestrate specific gene transcription patterns to regulate the lineage development, differentiation, and activation of IICs. This intricate process ultimately contributes to effective pathogen clearance and IICs’ healthy development and differentiation. To thoroughly elucidate the epigenetic mechanisms underlying the development and differentiation of IICs, this review first introduces the fundamental concepts and latest advancements in this field. We then delve into how the immune microenvironment or other signaling molecules shape the epigenetic landscapes of distinct IIC subsets during their lineage development and differentiation. Furthermore, we summarize how different epigenetic modification profiles mediate specific transcriptional patterns, thereby influencing the lineage development, differentiation, and activation of IICs in response to infections or injuries. Finally, we discuss several unresolved critical issues from the perspective of targeting epigenetic modifications to modulate the innate immune response. In summary, this review aims to uncover the molecular mechanisms underlying the development, differentiation, and activation of IICs from an epigenetic perspective, providing theoretical foundations for scientific and medical researchers pursuing disease treatments.