In a locked workroom at the University of Delaware Library, Amanda Daddona was sifting through boxes of 18th- and 19th-century documents last month when she stumbled upon an unexpected treasure.

Tucked amid obscure financial records and the minutes of Quaker meetings was an unmarked folder containing a letter written in Washington on Feb. 24, 1808.

Her eyes quickly fell on the distinctive signature at the bottom of the page: Thomas Jefferson.

"It was emotional for me," said Daddona, 22, one of two graduate students who are cataloging the archives of the Rockwood Museum, recently donated to the library by New Castle County.

"I've always loved Thomas Jefferson," she said. "He's the reason I got so interested in history. I recognized his signature. It was the most prominent part of the letter."

Daddona called fellow student Matthew Davis, 28, of Wilmington, to take a look.

"It's obviously not something you run into every day," Davis said. "It definitely validated what we were doing with the collection."

The letter, in neat cursive, was written by President Jefferson to Joseph Bringhurst of Wilmington in response to a missive from the physician announcing the death of John Dickinson.

Dickinson was a wealthy lawyer who had served as a militia officer during the American Revolution, a representative to the Continental Congress from Pennsylvania and Delaware, and a delegate to the Constitutional Convention of 1787. He also had been president of Delaware and president of Pennsylvania.

His close friend Bringhurst had cared for him in Wilmington during his last days.

"A more estimable man, or truer patriot, could not have left us," Jefferson wrote to Bringhurst. "Among the first of the advocates for the rights of his country when assailed by Great Britain, he continued to the last the orthodox advocate of the true principles of our new government and his name will be consecrated in history as one of the great worthies of the revolution."

The letter found by Daddona is in Jefferson's own hand. A duplicate, apparently created at the same time on a crude copying device called a polygraph, is held in the Library of Congress.

"I loved the line in the letter where he speaks of himself as a 'junior companion of his labors in the early part of our revolution,' " said Daddona, whose family lives in East Hartford, Conn. "It was very humble of him to say that. It showed what high esteem he had for John Dickinson."

In the letter and in other records contained in the Rockwood collection, "you really get the flesh and bones of what life was like back then," said Davis, a Bloomsburg, Pa., native.

The Jefferson letter "is definitely above and beyond what you expect to find in a collection of papers like that."

The Rockwood collection contains more than 200 boxes filled with thousands of documents, maps, letters, photographs, albums, diaries, deeds, and business records from the late 1600s through the late 1970s. Many of the older items have not been examined for decades.

Though historians were aware of the Jefferson correspondence, its discovery in the collection "opens up the story about the relationship" between Bringhurst and Dickinson, said Rebecca Johnson Melvin, librarian and coordinator of the manuscripts unit in the special collections department of the University of Delaware Library.

Bringhurst, who was named Wilmington's postmaster by Jefferson, and his wife, Deborah Ferris Bringhurst, were close friends of John and Mary Dickinson's. The Bringhursts named their daughter Mary Dickinson Bringhurst.

"It gives you a sense of the small circles of people in the Revolution and early Federal period," Melvin said.

"Even though the copy is available, when you find the original in the Bringhurst papers, you have the historical context," she said. "You see the connections to Delaware and understand the relationships of the people at the time."

Daddona is still savoring the moment of discovery. "It was quite an exciting day," she said.

The graduate students expect to finish processing the Rockwood collection by the end of the academic year.

"There's always the chance we will turn up something else," Davis said. "But it probably won't be this exciting."

Contact staff writer Edward Colimore at 856-779-3833 or ecolimore@phillynews.com.