MoCo’s Lost City: Triadelphia

by MCS Staff

Triadelphia (“three brothers”) was founded in 1809 by brothers-in-law Thomas Moore, Isaac Briggs, and Caleb Bentley, who were married to the Brooke sisters (Descendents of Robert Brooke, the founder of Brookeville).

“Born of the Patuxent River and then destroyed by it, the mill town Triadelphia knew years of glory as a leading Maryland industrial center.” – Sandy Spring Museum. Today the Patuxent River marks the NE border of MoCo, but between 1809 and the civil war it powered the mills that made Triadelphia a thriving industrial community. At the time, it was even larger nearby Rockville.
As planned; cotton, grist, saw, and plaster mills in the town were all powered by the river. It was the only town of its kind in Montgomery County, but nearby cities, like Ellicott City, were formed with the same purpose. So what happened to Triadelphia?

The same water that helped create the thriving town ended up destroying it. A flood in 1868 causes significant damage to Triadelphia and other surrounding areas. Almost every mill was completely destroyed except for the grist mill. Entire homes were even swept away. 

There were attempts to rebuild some of the other mills, but the Johnstown flood of 1889 completely destroyed everything that was rebuilt. At that point, steam power and gasoline had become far more popular. Railroads were used for transporting goods, so it was beneficial to build towns closer to the tracks, and the decision was made not to rebuild Triadelphia.
In 1943, WSSC completed construction of the Brighton Dam. This led to the complete submerging of what was left of the town. Not much remains of Triadelphia, but a graveyard that’s located on a hill overlooking the town did go untouched and a bell from 1837 that once called the mill hands in to begin work for the day can be found at Sherwood High School.
Featured photo courtesy of the Sandy Spring Legacy

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George October 26, 2020 - 4:20 pm

I didn’t get what the Johnstown Flood had to do with Triadelphia?

Billy bob October 26, 2020 - 9:00 pm

Probably the same weather that caused the dam to fail in Johnstown Road flooding to Maryland

Ken October 27, 2020 - 2:08 pm

Something like 11 inches of rain fell in the three days prior to the damn failing at the Hunt Club…I imagine similar conditions prevailed here…

Andy Bittner October 30, 2020 - 12:22 pm

It probably would have been better worded as, “The storm that caused the Johnstown flood.”

Gayle Priebe Andriani. October 26, 2020 - 8:49 pm

My Browns lived there. Now all buildings are under water. Glad the Cemetery is still there.

MDuvall October 27, 2020 - 5:20 pm

Hi Gayle, Any records of Duvall’s in Triadelphia, perhaps buried next to the brown’s? Investors visited the cemetery but many grave markers are in a poor state. Thx – Mark

Andy Bittner October 30, 2020 - 12:24 pm

Gayle… The buildings are not still there. When the reservoir was emptied a few years ago, I explored the site. The only remnant I might have seen within the shoreline of the lake was what might have been the remnants of an old mill race. The buildings were destroyed and removed as the valley was prepared for flooding.

Mike February 13, 2023 - 10:45 am

Andy- Was that when they did the repairs to Brighton Dam? I was wondering if Greenbridge Road, just north of the dam was how they accessed the Howard County side prior to Brighton Dam being built. I fished the reservoir a number of years before moving to Florida in 2010, the history surrounding the reservoir and it’s building have always intrigued me. I had a fisherman tell me there was a foundation from one of the old structures about 50 feet past the end of the Greenbridge boat ramp, don’t know if that is true or not. When I would fish the reservoir, I would look along the shoreline and imagine what the village looked like and it’s inhabitants engaged in everyday life. Is there any historical society or library that might have the information?

Mike February 13, 2023 - 12:47 pm

Andy, I used to fish Triadelphia regularly until I moved to Florida in 2010. I was told by a fisherman at the end of the Greenbridge boat ramp just up from the dam there is supposedly a foundation from one of the old buildings there, can’t vouch for it though. I have always thought the history of Triadelphia, both the village and the dam was quite interesting. When I would fish there I would sometimes imagine the city that once stood where the water is now and everyday life in the town.

Lena October 26, 2020 - 11:30 pm

Very interesting history! Can you write a piece to educate on the history of indigenous people/tribes who were here in the lands that we now call Montgomery County?

Ryan October 27, 2020 - 11:49 am

I’m not sure of the veracity of this, but I have heard that no indigenous people actually lived inside the confines of what is now Montgomery County, though they did hunt here, at least around the time of contact with the Europeans.

Andy Bittner October 30, 2020 - 12:26 pm

There were arrowheads and points found in and around what is now the Triadelphia lakebed. I know that much.

Gail Velez October 27, 2020 - 12:18 pm

A bit curious, if this is supposed to be a picture of Tridelphia which was completely destroyed by the Johnston flood in 1889, why is there a car in the picture.

MCS Staff October 27, 2020 - 1:03 pm

A few homes were still left standing in 1941 when the photo was taken. They’re now gone as well.


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