Energy Storage (ES) has been seen as a crucial element in active distribution networks. It facilitates a high penetration level of intermittent renewable energy in power systems thus provide several technical and economic benefits to the utility and consumer. However, given a high capital cost associated with ES, it is crucial to develop an effective planning strategy to avail the maximum benefit. This paper proposes a methodology to determine the optimal location and capacity of Community Energy Storage (CES) units by considering all their possible benefits and costs. The benefits are obtained from energy arbitrage, peaking power generation, energy losses reduction, Transmission and Distribution (T&D) system upgrade deferral, CO2 emission reduction and VAr support, while the costs include CES's capital, replacement and Operational and Maintenance (O&M) costs. A comprehensive cost-benefit analysis is conducted to identify the optimal Net Present Value (NPV), Discounted Payback Period (DPP) and Benefit Cost ratio (BCR) of CES investment starting at current year, year 2025 and 2035. Numerical results show that the proposed strategy is able to specify the optimal location and size of CES unit for maximizing the NPV. Some interesting findings are also discussed in the paper.