This excerpt taken from the EQR 8-K filed Sep 16, 2008.
Section 1. PRINCIPAL OFFICE. The principal office of Equity Residential (the Company) shall be located at such place as the Board of Trustees may designate.
Section 2. ADDITIONAL OFFICES. The Company may have additional offices, including a principal executive office, at such places as the Board of Trustees may from time to time determine or the business of the Company may require.