EARLY in the age of automobiles, the premier American sports car was produced in Mercer County. The Raceabout, among the country’s first sports cars and manufactured by the Mercer Automobile Company, a business founded by the legendary Roebling and Kuser families, debuted in 1910.

   In 1911 the Raceabout entered six races and won five of them. In 1914 a Hamilton mechanic named Eddie Pullen entered the Raceabout in the 403-mile American Grand Prize race. He became the first American to win the prestigious race, and Trenton held a parade for him where he received a medal from Mayor Frederick Donnely.

   ”We get excited today when a new cell phone comes out but 100 years ago people got excited about automobiles,” says Clifford Zink, co-author of a new 24-page booklet, Mercer Magic, that tells the car company’s story. “They were playthings for rich people. Thanks to Henry Ford, they became a common form of transportation.”

   The Mercer Automobile Company’s exclusive cars were never mass produced. Between 1910 and 1925, it made as few as 5,000 cars, including sedans, roadsters and limousines. Mr. Zink estimates of the 125 that still exist, 75 might be road worthy. He adds that in 2006 a Mercer, a generic term for any car made by the company, was sold at auction for $1.5 million. Jay Leno may be the Mercer’s most famous owner today.

   ”The people who own and restore them, they’re complete fanatics about authenticity and making them look as original as possible,” Mr. Zink says.

   The Mercer Centennial Rally will present between 15 and 20 Mercers at the Roebling Museum July 12. A number of the cars will also be presented during the Florence Patriotic Day Parade July 11.

   Karl Darby, a Roebling descendent who owns two Mercers and keeps one in his living room, will display his cars. “He has a great deal of enthusiasm for these cars,” Mr. Zink says.

   Mr. Darby and Tim Kuser assisted Mr. Zink in preparing Mercer Magic. It will be available to buy at the reunion. The name refers to a series of fliers Mercer Automobile Co. printed to summarize their racing success.

   Racing was one way to demonstrate a car’s reliability because pushing the car would produce flaws that would otherwise take time to appear. “You could show that your car was very durable and very fast,” says Mr. Zink.

   The Raceabout was capable of achieving 70 to 90 miles per hour at a time when nearly no roads were suitable for such speeds. The cars were marketed as having a dual purpose. “A gentleman could take one to the racetrack, race very successfully and then drive around the streets in the meantime,” Mr. Zink says.

   Mercers were expensive and people paid handsomely for them. “They are highly prized cars, because they were beautifully made,” Mr. Zink says. “The Roeblings were engineers. They had a general policy of doing everything well.”

   The builders of the Brooklyn Bridge, the Roebling family was “always on the lookout for new investments,” says Mr. Zink, a Roebling Museum consultant and author of Spanning the Industrial Age: The John A. Roebling’s Sons Company, Trenton, New Jersey, 1848-1974. (A new edition of the 1992 book is forthcoming, he says.)

   Mercer Automobile Co. was run respectively by John A. Roebling’s son and nephew, president Ferdinand and general manager Washington. The secretary-treasurer was John L. Kuser. The Kusers earned their fortune from a banking, bottling and brewing company.

   ”This was a time when there were tinkers all over this country and Europe who were starting car companies,” Mr. Zink says. “There were lots and lots of small companies making cars.”

   Washington Roebling enjoyed racing cars and was the major impetus for his family’s involvement, Mr. Zink says. “Here was this young man in his late 20s, the son of a wealthy family spending time with other rich families and having fun racing with this new technology called automobiles.”

   After Washington Roebling visited Europe to test drive the Fiat in 1912, he boarded the Titanic to return home. He was 31. After his death, the Roebling’s interest in cars began to decline, Mr. Zink says. By 1919, each of the company’s founders had died and, when World War I began, the Roeblings were overwhelmed with orders. The family sold their interest to Hare’s motors. The final Mercers were produced in 1925.

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  The Mercer Centennial Rally will be held at the Roebling Museum, 100 Second Ave., Florence, July 12, 11-4 p.m.. A number of Mercers will also be presented during the Florence Patriotic Day Parade, July 11, noon; www.roeblingmuseum.org