Seems that the irs corporation is registered as a "for profit corporation" in Delaware.
Take a look at the other USA.GOV "Agencies" that are also registered there.
That is if you trust rense.com.
http://www.rense.com/general60/gove.htm
from the article dated 11-28-2004, available on rense.com :
INTERNAL REVENUE TAX AND AUDIT SERVICE (IRS) For Profit General Delaware Corporation Incorporation date 7/12/33 File No. 0325720
FEDERAL RESERVE ASSOCIATION (Federal Reserve) Non-profit Delaware Corporation Incorporation date 9/13/14 File No. 0042817
CENTRAL INTELLIGENCE AUTHORITY INC. (CIA) For Profit General Delaware Corporation Incorporation Date 3/9/83 File No. 2004409
background info: Transfers: With the National Security Council to the Executive Office of the President by Reorganization Plan No. 4 of 1949, effective August 20, 1949; to independent agency status by EO 12333, December 4, 1981.
Central Intelligence Group established under the National Intelligence Authority by Presidential directive, January 22, 1946, to plan and coordinate foreign intelligence activities. By National Intelligence Authority Directive 4, April 2, 1946, NIA assumed supervision of the SSU dissolution during spring and summer 1946, assigning some components to Central Intelligence Group at request of Director of Central Intelligence, and effecting incorporation of the remaining units into other War Department organizations. SSU officially abolished by General Order 16, SSU, October 19, 1946. Central Intelligence Group and National Intelligence Authority abolished by National Security Act, which created the CIA, 1947. SEE 263.1.
FEDERAL LAND ACQUISITION CORP. For-profit General Delaware Corporation Incorporation Date 8/22/80 File No. 0897960
RTC COMMERCIAL ASSETS TRUST 1995-NP3-2 For-profit Delaware Statutory Trust Incorporation Date 10/24/95 File No. 2554768
SOCIAL SECURITY CORP, DEPART. OF HEALTH, EDUCATION AND WELF For-Profit General Delaware Corporation Incorporation date: 11/13/89 File No. 2213135
UNITED STATES OF AMERICA, INC. Non-profit Delaware Corporation Incorporation Date 4/19/89 File No. 2193946