The agreement by the owners of 75 percent of the property within a proposed district’s boundary is required to form a local historic district, including the Baltimore County Historic District. Any exterior modification or addition to a structure in a district, or any excavation, building, or demolition permit, is subject to approval by the Landmarks Preservation Commission. Historic rehabilitation tax credit programs from Baltimore County and the Maryland Historical Trust (MHT), the state agency for Historic Preservation, may be available to residential and commercial properties that qualify.