William Armstrong (1782-1865) - served four terms in the United States Congress, from 1825 to 1833, born in Lisburn
John T Mills (1817-1871) - justice of the supreme court in the Republic of Texas and Mills County, Texas, was named after him, born in county Antrim
Isaac Marston (1839-1891) - member of the Michigan state house of representatives and chief justice of Michigan state supreme court, born in county Armagh
Thomas Henry (1779-1849) - served three terms in the United States Congress, born in county Down
Robert Thompson Davis (1823-1906) - served three terms in the United States Congress, born in county Down
William Erigena Robinson (1813-1892) - assistant editor of the New York Tribune, served three terms in the United States Congress, born at Unagh, near Cookstown, county Tyrone
John George Warwick (1830-1892) - lieutenant governor of Ohio and member of the United States Congress, born in county Tyrone
These are just a few of the omissions in that particular subject area but they serve to make the point. The Dictionary of Irish Biography is a very useful and substantial resource but in relation to Ulster there are many signifciant omissions.