Redevelopment of the former Montgomery County Fairgrounds has slowly shifted from planning and fundraising toward visible construction.
The 38-acre site along South Main Street is now being developed as onMain, a long-term partnership between the University of Dayton and Premier Health that aims to create a walkable district focused on research, housing, and innovation. The project sits between the University of Dayton campus and Miami Valley Hospital and is intended to reconnect this area of the city with new streets, public spaces, and mixed-use development.
Today, a major new building is rising at the corner of South Main and West Stewart streets, while the site’s most recognizable historic structure, the Roundhouse, has already undergone stabilization and restoration work as part of the overall plan.
Redevelopment of the Former Dayton Fairgrounds
The University of Dayton and Premier Health purchased the former Montgomery County Fairgrounds property in 2017 with the goal of redeveloping it into a new urban district called onMain.
The vision for the site emphasizes walkability, sustainability, and a mix of uses including housing, employment space, and public gathering areas. Planning for the project included input from hundreds of community members and neighborhood stakeholders.
Rather than functioning primarily as a retail destination, the district is intended to be a place where people live, work, and collaborate, with businesses and amenities designed to serve the community. Plans also include public spaces, urban agriculture areas, and connections to regional bike trails and nearby neighborhoods.
Because the site covers nearly forty acres, the project will unfold in multiple phases over many years.
The OnMain Innovation Hub and How It Came Together
In August 2024 Governor Mike Dewine announced that Dayton and the fairgrounds site was selected for the state’s second Innovation Hub, intended to “bring together government, academia, and private sector industry partners” in order to “create digital technology that will drive advancements in aviation and national defense.”
The news release even referenced the “groundbreaking achievements of the Wright Brothers” and stated there would be $35 million in state funding from the Ohio Innovation Hubs Program, a local match of at least $23 million, and private sector funding of up to $37 million.
In October 2024, the City of Dayton approved $4 million in bonds for infrastructure improvements on the site.
An update in December 2024 said that the first phase “will focus on the southern strip of the 38-acre site along South Main Street, (and) is expected to create 170 rental housing units and a large building for research and innovation.”
Infrastructure Work and First Building at Main and Stewart
Infrastructure work began in 2025, including roadways, utilities, sidewalks, and landscaping including tree plantings. The City of Dayton granted spending $5.8 million to help with infrastructure work, which is continuing into 2026.
But the most exciting part of the first phase is now well underway at the northwest corner of South Main and West Stewart streets, where the initial building for the development is being constructed.
The 5-story, 120,000 square foot building with a striking, modern look will serve as an anchor for the district and house the Innovation Hub’s Digital Transformation Center, including research labs, offices, and flexible space designed to support emerging technology companies, university partnerships, and Air Force researchers.
Plans call for a building of roughly 120,000 square feet that can accommodate research teams, startups, and educational programs. The project represents an investment of about $73 million and is being built by Shook Construction.
Initial plans explained that the first phase would also include an outdoor plaza and gathering space, a canal park and retention basin with a perimeter walking trail, and other community spaces and amenities for a site that has long been empty and fenced off.
When complete, the broader OnMain redevelopment may include offices, housing, retail spaces, and parks spread across multiple blocks. A refreshed master plan for the site was released in February, 2026, with OnMain’s CEO Brian Heitkamp “suggesting thinking of onMain as a ‘land developer;” which “will develop ‘pads’ for construction on the former fairgrounds, build infrastructure and lease those pads to long-term users.”
Housing is expected to be the next building phase, possibly near the end of 2026.
Renovation of the Historic Roundhouse
Another major step in the redevelopment came during summer 2025, when work began to stabilize and refurbish the historic Roundhouse building.
The central role of the historic roundhouse is a key part of the overall project.
Part of the terms of the sale of the fairgrounds to the University of Dayton and Premier Health was to preserve the structure.
Renovation work was completed “to repair and paint the Roundhouse building’s exterior wood facade, including its sheathing, battens and trim.” The roundhouse was given new windows and doors that match the originals, and the whole job totaled $1.2 million, most coming from federal money from a previous appropriation bill due to the efforts of US Representative Mike Turner.
Future plans envision the building serving as a gathering space and focal point for public events within the development.
Early History of the Roundhouse and the Montgomery County Fairgrounds
The roundhouse, also referred to as the Octagon Building and the Exhibition Building, dates back to 1874, the same year the Fair Association was officially formed.
The first fair at the South Main Street fairgrounds location took place in 1856. (And the very first fair held in Dayton was in 1839 at Swaynie’s wagon yard on East First and Race St.)
By the 1870s the fairgrounds had become an established venue for agricultural exhibitions, entertainment, and community gatherings.
A picture from the 1874 fair depicts the “world’s fastest racehorse,” Goldsmith Maid, who set a new world trotting horse record which was “a mile in 2.18 minutes.”
One source said that “There was no room to move in the overflowing grandstand and grounds, so spectators hoisted themselves onto the tops of stables and cattle barns. The extra weight caused rooftops to give way, and the show cows found themselves with unexpected company” (source: Dayton Metro Library digital images).
The roundhouse building was designed that year as an exhibition hall where manufacturers and merchants displayed products of all types.
For the roundhouse’s first exhibition it showcased “household appliances, including heating and cooking stoves and grates, furniture, pianos and organs, sewing machines and jewelry.”
After that, it has hosted a variety of parties and special events, and the roundhouse was also the longtime home of the A.B. Hallum furniture store when it wasn’t fair season.
Even after the Montgomery County Fair moved to a new location in Jefferson Township in 2018, the Roundhouse remained one of the few surviving reminders of the fairgrounds’ long history.
You can visit the OnMain website for more information on the vision and progress of the project.
Historic image credits Dayton Metro Library
Original article with early OnMain development news was posted March 9, 2018. The article was expanded in 2024 and 2026.
I have a great story to share about my late grandparents winning a car at the fair in 1936. There is a beautiful picture of my grandmother in front of the car. My uncle who is 96 submitted it to Reminisce magazine and I will try to find my issue and send you a photocopy of the article.
I write you to find out the latest news about the fate of Roundhouse and will it remain standing. The area played a role in my Brookville, Ohio family history in the 1930;’s and I hope that the Roundhouse will not be demolished. I never got to know Dayton as an adult as I started college in 1972 and move to Georgia in 1979. I hope the Roundhouse can be incorporated into plans for the property. History is so important to preserve.
The Roundhouse still stands in Dayton. It look to be on good condition and is fenced off. I was looking for more information and came across this post, so wanted to give you an update.
Nicole, thanks for confirming that and I appreciate you sharing that memory Teresa!
There have been a lot of grand plans shared for the larger site and a lot of money committed, but I think there’s still a ways to go before anything actually happens. I do think that the Roundhouse will continue to be preserved but since the first phase appears to target the Main and Stewart intersection, it will probably be many years before it reaches it. Hopefully they invest sufficiently in keeping it maintained.
I also updated the article with major news of the last few years.
68-72 worked part time for ABHLlum. I worked in the round house n fine arts bldg. moving furn. _and selling some.
I knew bunch Of Chaminade Friends mostly from The East End. That worked there too.
He was a trip. I’ll tell you. !
The picture of the 1874. World’s Fastest Racehorse” (large size) has been displayed at the Golden Lamb, In Lebanon, OH for the past several years. . As a native Daytonian, I was thrilled when I first saw it. I immediately recognized the roundhouse and walked over to read its inscription to confirm it was on the Montgomery County Fairgrounds. I first saw it hanging in the handicapped restroom but it was moved. The last time I saw it was in the Black Horse Tavern, at the back of the room.