Elmer Lincoln Irey (1888 – July 19, 1948) was a United States Treasury Department official and director of the Internal Revenue Service's lead investigative unit during the federal tax evasion prosecution of Chicago mobster Al Capone.
Appointed Chief of the Treasury Department's Internal Revenue Service Enforcement Branch in 1919, Irey formed one of the most successful investigative teams in the history of American law enforcement with agent Frank J. Wilson leading the hundred-man unit of "T-men" in a three-year investigation against Capone's criminal organization the "Chicago Outfit". Despite attempted jury tampering and death threats against Wilson, Irey's investigation succeeded in the conviction of Capone for tax evasion in 1931.
During the Lindbergh kidnapping, some sources indicate that Irey insisted on tracking the serial numbers on the gold certificates used as ransom money (which ultimately led to the arrest and conviction of Bruno Richard Hauptmann). Other sources credit James W. Wilson.
Irey's "T-men" unit prosecuted over 15,000 people for tax evasion (with a 90% conviction rate), including Louisiana Gov. Huey Long and Chicago businessman Moses Annenberg, over the course of 27 years.
Named chief coordinator of all the Treasury Department's law enforcement agencies in 1937, Irey oversaw the operations of the U.S. Secret Service, the IRS Intelligence Unit, U.S. Customs, the Bureau of Narcotics, the Alcohol Tax Unit (predecessor to ATF), and the U.S. Coast Guard, until his retirement in 1941.
He wrote his autobiography, "Tax Dodgers" in 1942. He relates stories of how President Franklin D. Roosevelt (FDR) used the IRS to attack his political enemies. One was Andrew Mellon, who was Secretary of the Treasury during previous Republican administrations. Mellon was found innocent of all charges.
IRS agents under Irey began investigating Louisiana Governor and later Senator Huey Long during Hoover administration but suspended the investigation following the election of Franklin Roosevelt. After several months awaiting guidance from the new administration, Irey received a go-ahead to restart the investigation from Treasury Secretary Henry Morgenthau, Jr. In his biography, Irey related the personal interest and direct intervention of FDR in the investigation of Long, another of his political enemies who was considering running for President against Roosevelt in 1936. Several of Long's cronies were convicted, but Long was murdered in 1935 just weeks before U.S. Attorney Dan Moody planned to present evidence against him to a federal grand jury.
Another memoir of the IRS being used as a political weapon was written by Elmer Lynn Williams, which described the attack on William Malone, a Republican who ran for governor of Illinois.
Mr. Irey appears in the opening scene of the 1947 semidocumentary film T-Men, starring Dennis O'Keefe, explaining to the audience how the various enforcement agencies of the Treasury Department work together on the case they are about to see.

The main computer system of the Serious Organised Crime Agency is named Elmer, in his honour.