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...since the EXPERIENCED folks have done such a really good job of running the country! 51 years, 176 days Robert Byrd Democratic 49 years, 349 days Daniel Inouye Democratic 47 years, 307 days Patrick Leahy Democratic 47 years, 159 days Strom Thurmond (I) Democratic, Republican 46 years, 292 days Ted Kennedy Democratic 42 years, 0 days Orrin Hatch Republican 41 years, 307 days Chuck Grassley Republican 41 years, 305 days Carl Hayden Democratic 41 years, 59 days John C. Stennis Democratic 40 years, 10 days Ted Stevens Republican 39 years, 94 days Thad Cochran Republican 38 years, 55 days Fritz Hollings Democratic 38 years, 9 days Richard Russell Jr. Democratic 38 years, 3 days Russell B. Long Democratic 37 years, 307 days Mitch McConnell Republican 37 years, 6 days Francis E. Warren (I) Republican The 99th Congress (1985–1987) was the period in which most people from this list were serving together (all but Hayden, Russell Jr., Warren, Eastland, and Magnuson).