Tax Services
Portland, OR
Located in South Portland, Withum is a leading Portland CPA firm focused on accounting, tax and advisory services.
As a top 25 national firm, Withum’s dedicated team members serve organizations across industries that range from startups to global enterprises. We are a technology-driven firm helping the Portland community grow and thrive with services ranging from cybersecurity and forensics accounting to employee benefit plan audits and outsourced accounting services…plus a whole suite of advisory solutions that will level up your success. That’s the Power in the Plus!
(818) 789 1179
Portland Service Specializations
Assurance and Accounting
Cybersecurity
Forensic and Valuation Services
State and Local Tax
Outsourced Accounting Systems and Services (OASyS)
Oregon State and Local Tax Updates
Do you or your organization operate in multiple states? Do you own property in a variety of states? Oregon State and Local Tax (SALT) laws are always changing and understanding the nuances of the states that you own or operate in is challenging. In these Oregon resources, you’ll find just a dash of the most up-to-date details on rules and regulations as state and local tax changes happen by state!
Industries We Focus on in Portland
Beyond the Region
- Inside Public Accounting Top 100 Firms – 22nd Largest Nationally
- Accounting Today Top 100 Firms – 22nd Largest Nationally
- Great Place to Work® – Fortune Best Workplaces for Parents and Women
- Vault Top 25 Accounting Firm
Partner In Charge
Joseph M. Thiermann, CPAJoe is a partner with over 25 years of specialized audit experience with audits of defined contribution plans, defined benefit plans, health and welfare plans, labor organizations and not-for-profits. He conducts system-wide reviews, designs and implements accounting systems and works on special projects involving system design, expense reporting and compliance, often in conjunction with other professionals to resolve regulatory and general management issues for clients.
Joe is an avid public speaker, having presented at the Annual Conference of the International Foundation of Employee Benefit Plans (IFEBP), the IFEBP Accountants’ Institute and the Oregon Labor Law Conference, and even taught business courses to contractors.
Portland Leadership
Withum in the News
Chris Passmore Named Top Leader on Los Angeles Business Journal List for Fourth Consecutive Year
As partner-in-charge of Withum’s Los Angeles office, Chris plays a pivotal role in the Firm’s growth on the West Coast. With nearly 25 years of experience in the profession, he specializes in assurance and business consulting services to emerging and middle-market companies. In addition to serving technology companies and professional services firms, Chris holds an advanced-level certificate in 401(k)…
Kerra Diener Named as 2026 Los Angeles Business Journal Top 100 Accountant
Kerra Diener is a partner in Withum’s Los Angeles, CA office, advising multinational and multistate businesses on complex federal and state tax matters. Known for her specialized technical depth, she helps corporate and private clients across industries, including industrial and consumer products, real estate, theatre and entertainment and cannabis, with expertise spanning tax planning, compliance, M&A and consulting. The accolade…
CalCPA Names Withum Leaders to 2026 NorCal Top 50 Accountants
Top 50 Accountant Honorees at Withum Brandon Yip Brandon Yip is a partner who leads Withum’s Technology and Emerging Growth Services Team in the San Francisco Bay Area. He focuses on advising public and private companies on audit, regulatory and transactional matters while helping innovation-driven organizations scale. Deeply connected to Northern California, he supports the region’s technology and life sciences ecosystem…
Fortune Media and Great Place to Work Name Withum Among Best Workplaces in New York
Ranking at number 22 on the Large Business list, Great Place to Work recognized the Firm for its strong culture and team-centric approach, highlighting its distinctive benefits such as flexible schedules, childcare benefits and time off. The recognition also spotlighted Withum’s collaborative environment – prioritizing professional development, open communication, innovation and work-life balance, enabling team…
Withum Champions Veteran Initiatives and Community Impact
Wreaths Across America For more than five years, Withum has been an active participant in the Wreaths Across America initiative, which is championed by the Firm’s Veterans Team Member Resource Group (TMRG) and the Not-for-Profit Services Team. Wreaths Across America (WAA), is a national nonprofit dedicated to remembering fallen service members, honoring those who serve…
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