Mary Margaret O'Reilly (October 14, 1865 – December 6, 1949) was an American civil servant who served as the assistant director of the United States Bureau of the Mint from 1924 until 1938.

In 1933, the Mint gained its first female Director, Nellie Tayloe Ross, and despite initial mistrust between her and O'Reilly, they came to forge a strong bond.

When Margaret Kelly was commissioned Examiner of the Bureau of the Mint in 1911, the ripple of promotions in her wake included O'Reilly, who became adjuster of accounts.

Although the suggestion that the bureau eliminate the special coins, on which it lost money, came from Philadelphia Mint Superintendent Adam M. Joyce, and was approved by von Engelken, O'Reilly signed many of the letters to numismatists, and thus was blamed for the change in policy.

[8][9] When von Engelken resigned in February 1917, his successor was Raymond T. Baker, who foresaw that women would hold high government positions in increasing numbers, and gave O'Reilly a more public role.

[1][10] In December 1921, a public relations crisis over the design of the new Peace dollar had erupted while Baker was on a three-day trip by train to the West Coast.

Anthony de Francisci, designer of the coin, had included a broken sword on the reverse, which he intended as a sign of the end of war, but which many interpreted as a symbol of disgrace.

With Baker unreachable, O'Reilly realized the sword would have to be removed, and approached Treasury Undersecretary Seymour Parker Gilbert, who as acting secretary approved a revised design.

The Mint's Chief Engraver, George T. Morgan, skillfully removed the sword from the already-prepared coinage hubs even before Baker cabled his own approval of the revised design he had not seen.

[b] O'Reilly did keep a close eye on coinage operations, warning the San Francisco Mint in November 1931 that it had produced fewer than 200,000 nickels, a figure that if allowed to stand would have resulted in the issue being hoarded by collectors.

[15] President Franklin Roosevelt (FDR) appointed former Wyoming governor Nellie Tayloe Ross as Mint Director, the first woman to hold that position.

When the Treasury Department issued regulations allowing such coins to be surrendered at branches of the Federal Reserve Bank, O'Reilly sent out a memorandum over her signature as acting director noting that the Fed had no facilities to accept any gold other than bars with a government stamp.

[18] Burdette points out that the gold regulations showed a lack of basic Mint knowledge both by Roosevelt's appointees and the holdover senior officials from the Hoover administration.

Ross undertook a heavy travel schedule, visiting Mint facilities, making speeches backing Roosevelt, and campaigning for Democratic candidates in Wyoming.

[19] The two women carried on a businesslike but warm correspondence during these times, with O'Reilly writing to Ross (who had embarked on a tour of the mints) "I am so anxious to have your mind at ease about the office here [in Washington] that I have resorted to rather frequent telegrams.

Her knowledge of bureau affairs was so extensive, and was so badly needed, that she was exempted from mandatory retirement by special order of President Roosevelt, at the request of Ross, giving O'Reilly an extra year in the Mint Service.

[21] Roosevelt approved a similar extension in 1936, a distinction considered so significant that Treasury Secretary Henry Morgenthau Jr. hosted a luncheon in her honor.

Her New York Times obituary recalled that when she had been granted the first extension by Roosevelt, reporters had sought to interview her, only to be met with the following statement: I am deeply grateful to the President for his extreme kindness.