Maintained as a state historical park, the site was designated a National Historic Landmark for its significance. The State of Ohio purchased the land and made it Ohio's first state park in 1891. In addition, this is part of the Hopewell Ceremonial Earthworks, one of 14 sites nominated in January 2008 by the U.S. Department of the Interior for potential submission by the United States to the UNESCO World Heritage List.
The Fort Ancient earthworks were built in at least three stages over an estimated 400-year period. The shoulder blades of deer, split elk antlers, clam shell hoes, and digging sticks were used to loosen the dirt, and baskets holding 35 to 40 pounds were used to carry and distribute the soils in building the earthworks. Archaeologists estimate the total volume of earth in the walls at 553,000 cubic yards (423,000 m3).
In 1809 the Philadelphia Port Folio published the first map and description of Fort Ancient. The accounts of the site by Atwater  and Warden  several years later are nearly identical to the 1809 report and map. The site was visited and surveyed in by John Locke in 1843. In Edwin Hamilton Davis and Ephraim George Squier's Ancient Monuments of the Mississippi Valley, they described Fort Ancient as "one of the most extensive, if not the most extensive, work...in the entire West", regarding its size.
Warren K. Moorehead conducted some of the initial excavations at Fort Ancient in 1887 and published his research in 1891 in the book Fort Ancient: Great Prehistoric Warren County Ohio. Additional research was conducted by William C. Mills in 1908  and Richard Morgan and Holmes Ellis in 1939-1940.
More contemporary research includes the following:
From 1982 until her untimely death in 1991, Patricia Essenpreis conducted a series of excavations that included the re-excavation and examination of embankment wall cuts conducted by Richard Morgan. These excavations demonstrated that the embankment walls were built in multiple stages and that post structures were documented at the base of the walls. She also examined the Gateway 13 exterior spur where she found evidence of bladelet manufacturing. Her final project involved the excavation of a pavement and structure on the exterior of the earthworks near the Twin Mound complex. Here, she documented a three-level limestone pavement with household or domestic activity at the lowest level.
From 1987 through 2006, Robert Connolly collaborated with and then continued the research projects initiated by Patricia Essenpreis. His initial work involved taking Essenpreis's "canons of construction" to develop an "architectural grammar" of earthwork elements, demonstrating their intentional and precise placement throughout the Fort Ancient complex. In 1995 and 1996 Connolly directed the investigation of embankment walls and a large interior space of the North Fort of the earthwork in advance of a new museum construction. The embankment wall excavation confirmed Essenpreis' conclusion of multiple construction levels, but added a level of complexity in alternate basket loads of different soils in the construction, many features below the embankment wall, and a three-level limestone pavement on the exterior of the wall that contained a cache of burnt animal bones. Excavation in the North Fort interior space revealed the presence of 10 habitation structures.
Beginning in 2006, Robert Riordan conducted excavations in the North Fort of the earthwork complex that revealed a complex series of posts and activity areas, some with intense burning. Riordan named the Moorehead Circle after the archaeologist who conducted early excavations at the site.
Some archaeologists originally thought the site was created to provide shelter against enemies. However, that interpretation is now discounted as the site presents anomalies inconsistent with defensive use such as:
Ditches are located inside the walls, rather than outside as a means of defense.
The 84 gateway openings in the walls could not have been defended in case of attack.
Evidence has not been found for the number of occupants necessary for a significant defense force.
Based on the total corpus of archaeological research, the current functional interpretation is that the walls were designed for social, economic, political and ceremonial purposes. Research demonstrates the site architecture was aligned with significant astronomical events. In the Northeast corner of the complex, four circular stone-covered mounds are arranged in a square. The southwest mound of the four is interpreted to have functioned as a point that aligned with gateway openings in the embankment walls to mark significant solar and lunar events.
The site now includes a 9,000-square-foot (840 m2) museum covering 1500 years of American Indian heritage in the Ohio Valley. Topics include North America's earliest people, the development of agriculture, and the impact of Europeans who migrated to the area and came into conflict with the Native Americans then living in region. The Museum also contains a classroom, a research area, and a gift shop. The site is open to the public Tuesday-Saturday from 10:00 AM to 5:00 PM and Sunday 12:00 - 5:00 PM April through November; weekends only from December through March.
The Historic Era Fort Ancient Village
Stone building from 1802 operated as the Cross Keys Tavern from 1809-1820
In the 1800s to early 1900s a village existed on the eastern bank of the Little Miami River, at the base of the Fort Ancient Earthworks. The village once had a post office (1846), hotel, blacksmith shop and other businesses and residences. The village no longer exists, but is currently the home of a canoe livery and a private campground.
^Moorehead, Warren K. Fort Ancient: The Great Prehistoric Earthwork 1891, AMS Press.
^Mills, William C. (1908) Field notes from 1908 excavations at Fort Ancient. Ms. on file, Ohio Historical Society, Columbus Ohio.
^Morgan, Richard and Holmes Ellis (1939-1940) Field Notes from 1939 & 1940 Excavations at the Fort Ancient State Memorial. Ms. on file, Ohio Historical Society, Columbus
^Connolly, Robert (1996). Middle Woodland Hilltop Enclosures: The Built Environment, Construction and Function. Ann Arbor: University Microfilms.
^Connolly, Robert (1998) The Architectural Grammar of Middle Woodland Hilltop Enclosures: Fort Ancient as a Case Study. In Ancient Earthen Enclosures of the Eastern Woodlands, edited by Lynne Sullivan and Robert Mainfort, University Press of Florida, Gainesville.
^Connolly, Robert and Lauren Sieg (1997). The Gateway 84 Embankment Wall. Volume II, 1995 Report of Investigations at the Fort Ancient State Memorial. copy on file, Ohio Historical Society, Columbus.
^Adrienne, Lazazzera (2004). Hopewell Household Variation at the Fort Ancient Site. In The Fort Ancient Earthworks, edited by Robert P. Connolly and Bradley T. Lepper, Ohio Historical Society. pp. 84–106.
^Robert, Riordan (2015). The End. In ‘Building the Past: prehistoric wooden post architecture in the Ohio Valley-Great Lakes,’ edited by Brian G. Redmond and Robert A. Genheimer, University Press of Florida, Gainesville. pp. 126–145.
^Connolly, Robert (2004) Time, Space, and Function at Fort Ancient. In The Fort Ancient Earthworks: Prehistoric Lifeways of the Hopewell Culture in Southwestern Ohio, edited by Robert P. Connolly and Bradley T. Lepper. Ohio Historical Society, Columbus.
^Romain, William (2004) Journey to the Center of the World: Astronomy, Geometry, and Cosmology of the Fort Ancient Enclosure In The Fort Ancient Earthworks: Prehistoric Lifeways of the Hopewell Culture in Southwestern Ohio, edited by Robert P. Connolly and Bradley T. Lepper. Ohio Historical Society, Columbus. pp. 66-83.
^Essenpreis, Patricia and David Duszynski (1989) Possible Astronomical Alignments at the Fort Ancient Monument. Paper presented at the 54th Annual Meeting of the Society for American Archaeology, Atlanta.