List of United States Senators in the 90th Congress by seniority

This is a complete list of members of the United States Senate during the 90th United States Congress listed by seniority, from January 3, 1967 to January 3, 1969.

Order of service is based on the commencement of the senator's first term. Behind this is former service as a senator (only giving the Senator seniority within his or her new incoming class), service as Vice President, a House member, a Cabinet secretary, or a governor of a state. The final factor is the population of the senator's state.

Senators who were sworn in in the middle of the two-year congressional term (up until the last senator who was not sworn in early after winning the November 1968 election) are listed at the end of the list with no number.

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