Source: http://www.taxhistory.com/crs/15.html
Timestamp: 2019-04-19 06:54:08+00:00

Document:
The Department of the Treasury is an office attached to the seat of government.77 The IRS is a part of the Department of the Treasury.78 Therefore the IRS must have its office in the District of Columbia unless otherwise expressly provided by law. The IRS does have its national headquarters within the District of Columbia.
73 4 U.S.C. § 71--78.
74 4 U.S.C § 72.
75 Ch. 28, 1 Stat 130, lst Cong., 2nd Sess. (July 16, 1790). The Act established Philadelphia as the temporary seat of government until the first Monday in December of 1800 when the seat of government would become the District of Columbia.
76 See, Ch. 35, 1 Stat. 145, lst Cong., 2nd Seas. (August 4,1790).
77 See, 31 U.S.C. § 301(a).
78 See, 26 U.S.C § 7802.
79 26 U.S.C. § 7621.
80 26 US.C. § 7803.

References: § 71
 § 72
 § 301
 § 7802
 § 7621
 § 7803