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William Colgin


555 17th Street, Suite 3200, Denver, CO 80202
25 South Willow Street, Suite 200, P.O. Box 68, Jackson, WY 83001

Bill represents corporate taxpayers in complex, high-stakes federal tax controversies and tax litigation with significant implications for his clients’ bottom line.

Bill litigates in the US Tax Court, federal district courts, state courts, and appellate courts throughout the country. His cases and controversies typically involve high dollar amounts and tend to include international tax, transfer pricing, intellectual property, economic substance, and other high-profile areas of tax dispute.

Bill began his tax litigation career as a trial attorney in the Tax Division of the US Department of Justice and he draws on that experience to represent clients in complex Internal Revenue Service (IRS) examinations and appeals, anonymous IRS disclosure disputes negotiations, and coordinated resolution of multistate state tax issues. Bill continues to defend clients in federal criminal and civil tax investigations by the Tax Division of the US Department of Justice or the US Attorney’s Offices around the country.

Prior to joining Holland & Hart, Bill was a partner at Morgan Lewis.


Tax Litigation and Controversy
  • High profile tax litigations involving deficiency and refund suits
  • Examination defense involving complicated and contentious issues
  • Extensive IRS Appeals negotiations
  • Anonymous IRS disclosure disputes
  • Qui Tam suits involving tax-related claims
  • False Claim Acts suits, both single-state and multistate
  • Coordinated management and resolution of multistate tax issues, including amnesty programs


Bar Admissions

Court Admissions


  • Chambers USA: America’s Leading Lawyers for Business, Litigation: General Commercial, Colorado; Wyoming, 2019
  • Chambers USA: America’s Leading Lawyers for Business, Tax, California, 2008-2018
  • Chambers USA: America’s Leading Lawyers for Business, Tax: Controversy, Nationwide, 2008-2018
  • The Legal 500 US, Tax – US Taxes – Contentious, 2011–2015, 2017

Professional and Civic Affiliations

  • California Bar, Executive Committee, Taxation Section, Past Vice Chair
  • Tax Court Pro Se/Pro Bono Program, San Francisco, California, Past Director
  • American Bar Association, Tax Section, Court Practice and Procedure Committee, Technology Subcommittee, Past Chair
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