Chief Trust Officer

JoAnn Dickinson, JD, CTFA

JoAnn was born and raised in South Dakota.  While running her own business for 22 years, she attended the Univeristy of South Dakota law school and received her Juris Doctorate in 1993.  From 1994 to the present, JoAnn has been a trust officer with First Dakota National Bank, Security National Bank, Great Western Bank, Citicorp Trust, Meta Trust and Sterling Trustees.


In 2008, JoAnn attained the professional designation of Certified Trust Financial Advisor (CTFA).  In addition to trust administration, she has extensive training and experience in Employee Benefits (pensions, 401k, etc).


JoAnn is a member of the South Dakota Bar Association and a member of the Sioux Falls Estate Planning Council.

Trust Counsel

Isabel Miranda

Isabel has over 30 years of experience in helping families preserve, manage and transfer their wealth. Her practice is focused on multi-generational wealth transfer planning, philanthropic planning and administration, family governance and trust and estate administration. Isabel serves as trust counsel to Argonne Trust Company, LLC. She also serves as Of Counsel to GluckWalrath, LLP where she consults on Trust and Estate matters. In addition, she was previously managing partner of the Trust and Estate practice at DeCotiis, Fitzpatrick, Cole & Wisler, LLP and Senior Vice President and Director of U.S. Trust Company of New Jersey. At U.S. Trust, she managed the trust business, served as Chief Trust Officer, was a member of the Board of Directors, and chaired the Personal Administration and Investment Review Committee. Prior to joining U.S. Trust, she was Vice President and Director of The Citibank Private Bank, where she headed the domestic personal trust business. In that role, she oversaw a national team of over 125 estate planning, investment and trust professionals in New York, Florida, California and South Dakota. Isabel served as Chair of Citicorp Trust of Florida, N.A. and Citicorp Trust of California, N.A. In addition, she founded Citicorp Trust South Dakota, which enhanced the corporation’s trust offering for ultra high net worth families.
Ms. Miranda’s goal is to counsel families seeking to transfer wealth in a manner that is not only administratively efficient but, more importantly, also conducive to family harmony and open communication. 
Isabel is a member of the American Bar Association, Real Property, Probate and Trust Section, Committee on Non-Tax Estate Planning Administration Issues, and Ethics and Mediation Committee; the New York Bar Association, Trust and Estate Section, Committee on Practice and Ethics, the Society of Trust and Estate Professionals, and serves on the Board of Directors for the Collaboration for Family Flourishing, a multi-disciplined group of professionals whose goal is to assist families to thrive across multiple generations.

Isabel served as Chair of the University of Medicine and Dentistry of New Jersey from 1998-2002 during which period the University undertook its largest capital campaign adding more than 500,000 square feet of new research space to expand the University’s research capabilities. In this role, Ms. Miranda served on the Executive Committee of the UMDNJ Foundation, and the board of directors of Robert Wood Johnson University Hospital. She also served on the Board of Directors of the Executive Women of New Jersey and the Women’s Political Caucus of New Jersey.
Ms. Miranda received her undergraduate degree cum laude from Fordham University, College of Business Administration and her Juris Doctor from St. John’s University School of Law. She is a member of the Bars of New Jersey, New York, and the United States Supreme Court.

Trust Marketing Officers

Monroe M. "Roey" Diefendorf, Jr., MI, CLU, ChFC, CFP, RFC, CIMA, CAP


Active since 1970, Roey is the 4th generation of his family in the business and was CEO of Diefendorf Capital Planning Associates until 2/7/2014, when he launched 3 Dimensional Wealth Advisory, LLC. Following his graduation from Deerfield Academy, he received a BA in Psychology from Bucknell University. He went on to obtain a Master's Degree in Insurance from Georgia State University, with a major in Estate Planning and a minor in Pension Planning. In 1976 and 1983, he received the designation of Chartered Life Underwriter (CLU) and Chartered Financial Consultant (ChFC) respectively from the American College, Bryn Mawr, PA. In 1992, the designation of Certified Financial Planner (CFP) was granted from the College of Financial Planners in Denver, CO. In addition, Roey has been admitted as a "CFP Practitioner." In March 2001, he was awarded the designation of Registered Financial Consultant (RFC). In 2003, he attended the Wharton School of Business and successfully attained the Certified Investment Management Analyst (CIMA) designation and in 2006, the Certified 3 Dimensional Wealth Practitioner(C3DWP) designation was added. In 2010, Roey added the professional designation of Chartered Advisor in Philanthropy (CAP) from The American College.


As an industry leader, Roey has co-authored three books: Wealth: Enhancement & Preservation - 1995 and 21st Century Wealth - 2000. In June 2005, his third book, "3 Dimensional Wealth: A Radically Sane Perspective On Wealth Management" was published. In 2014, he released his latest book, “A Better Way: Using Purposeful Trusts To Preserve Values & Valuables In Perpetuity.”  Over the years he has been a speaker at several international industry conferences and has made several guest appearances on the Cable TV program, "Dollars & Sense." In January 2003, Roey was interviewed by Forbes Radio, which "aired" on over 192,000 flights on American Airlines. Roey appeared as a guest on Alexander Haig's, World Business Review which was broadcast on CNBC in November 2005 and on United Airlines Inflight Television.


In June of 2008, Roey and his daughter, Emily addressed 8,400 members of the Million Dollar Round Table at their Annual Meeting in Toronto. The message was inspired by Emil's philanthropic efforts with orphans in Zambia. Roey's passion is consulting in the areas of "Family Wealth Counseling" and "Philanthropic Estate planning". As CEO, he is a member of the Kingdom Advisors and a charter member of The International Association of Advisors in Philanthropy(AiP). In addition, Roey is the founder, registered principal and a registered representative of Sterling Monroe Securities, LLC, (Series 6, 7, 24, 51 & 63) and a member of the Investment Management Consultants Association(IMCA) and the president of the NYC Chapter's board of directors along with membership in the National Association of Independent Broker Dealers (NAIBD).  Roey was an early adapter as a Registered Fiduciary (RF) and has required each of his senior advisors to adhere to these standards.  As a charter member of the Purposeful Planning Institute, Roey's commitment to "values based" planning led him to create Argonne Trust Company, a South Dakota non-depository bank/trust company. In addition, he is a Trust Marketing Officer with Argonne Trust Company, Inc..

In 2001, Roey's Registered Investment Advisory firm,
Consolidated Portfolio Review Corp. was one of 10 recipients nationwide to receive the "Fleet Bank Small Business Leadership Award," recognized for our significant revenue growth. In 2006, Roey was selected as a Semi-finalist in the prestigious Ernst & Young Entrepreneur of the Year awards. He was nominated for the Loren Dunton Award for the International Association of Registered Financial Consultants, the Charles R. Schwab IMPACT award and a finalist in the New York Enterprise Report Small Business award. In 2009, Roey was honored as part of the inaugural class of the "50 Around 50" award by the LI Business News. On the technology front, Roey is the founder of Megethos3, LLC, a business process management software that is the backbone to the Diefendorf organization. In their 2010 Northern Hemisphere competition, Gartner & 1 to 1 Media awarded their CRM Excellence Award to Roey/Megethos3 for "Efficiency." Former winners include: Accenture, Caterpillar Tractor, and e-harmony. In 2011, Roey was one of the judges for the CRM Excellence Award, reviewing case studies for Europe, the Middle East, Africa, along with North, Central and South America.


Thomas C. Palumbo, CLU, ChFC, C3DWP, CRPS, CAP

A veteran financial planner, Tom has been with the Diefendorf organization since 1988. He specializes in personal financial planning for individuals as well as small business planning for entrepreneurs. After graduating from Long Island University at C.W. Post with Magna Cum Laude, he matriculated in the American College, Bryn Mawr, PA. In 1995 and 1996 he received the designations of Chartered Life Underwriter (CLU) and Chartered Financial Consultant (ChFC). In 2005, Tom joined the ranks of "total wealth managers" with the attainment of the Certified 3 Dimensional Wealth Practitioner (C3DWP)

Tom is active in the charitable /non-profit arena and is a member of the International Association of Advisors in Philanthropy. In 2011, he attained the designation of Chartered Advisor in Philanthropy (CAP) from the American College. An additional area of expertise is in retirement planning. Tom has his Chartered Retirement Plans Specialist (CRPS) from the College of Financial Planning which enabling him to consult in the qualified plan marketplace.

Tom is a registered representative of Sterling Monroe Securities, LLC (Series 7 & 63) and a Registered Fiduciary (RF). He is a Trust Marketing Officer with Argonne Trust Company, LLC.

Jeffrey A. Higgs, CLU, CFP, C3DWP


Jeff is a graduate of Davidson College. With a BA in History, he has decided to follow in his grandfather's footsteps in the Financial Services industry. Jeff joined the firm in 2008 as a Registered Representative with Sterling Monroe Securities, having passed his Series 7, 53 & 66 with FINRA along with his Life, Health & Variable Annuity licenses. 

Jeff is a graduate of the CFP degree program at New York University and in 2011 he was granted the Certified Financial Planner (CFP) designation. In addition, he has attained the 3 Dimensional Wealth Practitioner (C3DWP) designation, as well as, the Chartered Life Underwriter (CLU) designation.
He is currently enrolled in the Certified Trust and Financial Advisor program through the National Bankers Association


Jeff is the Secretary and Trust Marketing Officer with Argonne Trust Company, LLC.



South Dakota Trust Administration Office

Argonne Trust Company, Inc.

4418 S. Technology Drive

Sioux Falls, SD 57106



(605) 274-3336



Or use our contact form.


Business Hours

9-5 CST

Print Print | Sitemap
© Argonne Trust Company

This website was created using 1&1 IONOS MyWebsite.