Nikolaevsk is in Kenai Peninsula Borough in Alaska. The waters of the Gulf of Alaska and Prince William Sound border the borough on the south and east with the dramatic Chigmit Mountains of the Alaska Range rimming the borough to the west. The Cook Inlet divides the borough into two land masses. The peninsula itself encompasses 99 percent of the borough's population and most of the development. The Kenai Mountains run north and south through the peninsula, contrasting to the lowlands lying to their west. The west side of the Inlet is sparsely inhabited, with the village of Tyonek being the largest populated settlement. The boundaries of the borough encompass a total of 25,600 square miles, of which 15,700 square miles are land. In comparision, the total land mass of the borough equals that of Massachusetts and New Jersey combined. However, the total borough population is less than 1/400th of that same area.