| W 90.1 | Tank Corps (1918-1919) |
| T 64.1 | Tax Advisory Staff (1949-1953) |
| Ju 11.1 | Tax Court of the United States (1942- ) |
| LC 36.1 | Technical Information Division (1954-1961) |
| A 106.101 | Technical Information Systems (1978-1981) |
| T 68.1 | Technical Staff Office (1947-1953) |
| C 1.202 | Technology Administration (1988-2007) |
| EP 10.102 | Technology Innovation and Field Services Division (1990- ) |
| EP 7.1 | Technology Transfer and Outreach (1971- ) |
| NA 1.1 | The National Academies (1863- ) |
| P 11.1 | Topography Division (1885-1936) |
| HE 20.7901 | Toxic Substances and Disease Registry Agency (1992- 1995) |
| L 34.1 | Training and Employment Service (1969-1971) |
| W 85.1 | Training Camp Activities Commission (1917-1919) |
| L 12.1 | Training Service (1918-1919) |
| GS 8.1 | Transportation and Communications Service (1961- 1972) |
| P 10.1 | Transportation Bureau (1949-1970) |
| TD 1.202 | Transportation Security Administration (2001-2003) |
| HS 4.302 | Transportation Security Administration (2003- ) |
| W 98.1 | Transportation Service (1919-1920) |
| T 40.1 | Treasurer of the United States (1789-1940) |
| S 9.2 | Treaties |
| M 104.1 | Troop Information and Education Division (1947-1949) |
| D 107.1 | Troop Information and Education Division (1949-1954) |
