Highlands Conservation Reauthorization Act of 2021 This bill extends through FY2028 the Highlands Conservation Act, which provides for land conservation in Highlands states (i.e., Connecticut, New Jersey, New York, and Pennsylvania). The bill authorizes the Fish and Wildlife Service to add a municipality to the Highlands region upon the request of a Highlands state. The bill revises the way in which land is identified for conservation to require using the best available science and geographic information systems. The bill allows political subdivisions of states to enter into agreements with the Department of the Interior for land conservation projects. A Highland state that receives funds for a land conservation partnership project may not use more than 5% of the funds to administer that project. The bill extends through FY2028 Forest Service and other Department of Agriculture programs to conserve land and natural resources in the Highlands region.