Multi-processor core three-dimensional (3D) integrated circuits (ICs) (3DICs) and related methods are disclosed. In aspects disclosed herein, ICs are provided that include a central processing unit (CPU) having multiple processor cores (“cores”) to improve performance. To further improve CPU performance, the multiple cores can also be designed to communicate with each other to offload workloads and/or share resources for parallel processing, but at a communication overhead associated with passing data through interconnects which have an associated latency. To mitigate this communication overhead inefficiency, aspects disclosed herein provide the CPU with its multiple cores in a 3DIC. Because 3DICs can overlap different IC tiers and/or align similar components in the same IC tier, the cores can be designed and located between or within different IC tiers in a 3DIC to reduce communication distance associated with processor core communication to share workload and/or resources, thus improving performance of the multi-processor CPU design.