This legislation, titled the "Shenandoah Valley Battlefields National Historic District Boundary Expansion and Partnership Act of 2026," significantly expands the geographic scope of the Shenandoah Valley Battlefields National Historic District. It amends the original 1996 Act to include Rockbridge County, Virginia , and Berkeley, Jefferson, and Morgan Counties, West Virginia , thereby extending the district beyond the Commonwealth of Virginia. This expansion aims to incorporate additional historically significant lands and interests into the protected area. The bill also reinforces the district's unique partnership model for management and administration, ensuring it operates as a distinct National Historic District. It mandates that the management plan be updated to address new areas and resources, while explicitly stating the district will not be subject to administrative provisions or funding formulas of the National Heritage Area System. Furthermore, it authorizes substantial appropriations, including $1,250,000 annually for operations and maintenance, and $2,500,000 annually for grants, technical assistance, and land acquisition from willing sellers through fiscal year 2033, guaranteeing continued funding and eligibility for National Heritage Area assistance. The Secretary of the Interior is also directed to report on replicating this successful partnership model in other National Park System locations.