The Largest SEO Companies in the U.S. in 2023

Updated April 2023.

Company size may not be the first factor you consider when it comes to choosing an SEO agency to work with, but it’s an indicator that a company is successful, organized, and has the resources to make your campaign a success. Often, firms that describe themselves as “SEO agencies” are small 1–5 person companies that are able to provide technical advice and backend updates, but don’t have the staff necessary to manage a multifaceted campaign. A firm that’s among the largest in the US will necessarily have a proven track record and be a reasonable option for businesses looking to outsource their SEO.

Because SEO is such a wide field, we’ve separated our list into 10 different niches. We’ve chosen to only list companies that have a laser focus on their particular niche rather than creating a simple list of the largest companies that happen to offer SEO as a service.

The Largest SEO Companies In The U.S. in 2023

For Thought Leadership-Based SEO – First Page Sage

First Page Sage is the largest overall SEO firm in the US, having attained its growth from continual specialization within the field of SEO, as opposed to the more typical agency trajectory of expanding horizontally into other marketing services.

The firm’s strength is combining SEO and thought leadership—a high quality form of content marketing—to turn its clients’ websites into Google-trusted industry resources, essentially automating lead generation for them. Most of its clients are in technical B2B industries such as SaaS, IT, and manufacturing, with clients including Cadence Design Systems, Logitech, and US Bank.

Their campaigns are comprehensive, consisting of SEO strategy, keyword research, technical SEO, content marketing, analytics, marketing attribution, and detailed reporting. 

Location: San Francisco, CA
Founded: 2009
Price Range: $$$
Services: SEO, Content Marketing, Web Design

For Small Businesses & Startups – Boostability

SEO is a long-term investment, and success in a small campaign can lay the foundation for a more comprehensive SEO campaign later on. However, small businesses and startups tend to have tight budgets, so an agency’s flexibility in being able to scale campaigns up and down is important. 

Boostability is the largest SEO firm that specializes in providing services to small businesses. They have low-cost packages that are designed specifically for companies that are just getting started, are in low-competition markets, and not yet ready to post blog content regularly. They also provide solutions for scaling businesses, so they can grow with their clients. Small business clients of Boostability include Bloom Studios, KIARO Computer Solutions, and Peterson Family Orthodontics.

Location: Lehi, UT
Founded: 2009
Price Range: $
Services: White Label SEO, SMB SEO, Web Design

For Multilingual SEO – Duffy Agency

Multilingual SEO is a difficult field: not only is translation an incredibly nuanced process, but SEO adds keyword strategy, search intent, and content creation into the mix. It gets further complicated when your company is in a technical B2B market, as you need a firm that understands how people use specialized jargon in their searches.

Duffy Agency specializes in providing SEO, online marketing, and social media marketing services to companies who have brands with international reach. They’ve worked with clients in fields ranging from Consumer Foods to Medical Services, and their past clients include Napapijri, Cavidi, and the United Nations World Food Programme.

Location: Dover, NH
Founded: 2009
Price Range: $$$$
Services: International SEO, Strategic Consulting, Online Brand Management

For Local SEO – ReachLocal

Not all companies need to compete nationally. A construction firm based in a single city, for instance, will gain nothing from being seen by searchers across the country. Instead, they can focus all of their efforts on geotargeted keywords which are both lower competition and much more likely to lead to a sale.

ReachLocal is the largest SEO agency with a focus on increasing local search visibility. They specialize in working with inherently location-bound companies in industries such as real estate, home services, and automotive sales and service, and their clients have included TGM Associates, Mr. Rooter, and Central Washington University.

Location: Woodland Hills, CA
Founded: 2004
Price Range: $$
Services Offered: Local SEO, PPC Marketing, Marketing Automation

For Amazon SEO – Seller Interactive

Google accounts for over 90% of all general search engine traffic, which is why nearly all SEO agencies dedicate themselves to understanding the nuances of Google’s algorithm. But for B2C eCommerce companies, making it to the top of Amazon’s search results is just as important as reaching the first page of Google.

In 2023, Seller Interactive is now the largest Amazon-focused SEO agency in the US. They’ve been helping businesses manage their AMS accounts since 2012, and have had particular success partnering with companies in the consumer technology, food &  beverage, and cosmetics industries. 

Location: Markham, Ontario
Founded: 2012
Price Range: $$
Services Offered: Amazon SEO, Amazon Account Management, Demand-Side Platform Advertising (DSP)

For Full-Service Enterprise Digital Marketing – Epsilon

Enterprises not only need to ensure that their marketing partner is familiar with enterprise-specific SEO strategies, but because of their size and entrenched processes, often find that they need to find a single agency to handle all of their digital marketing.

Epsilon combines SEO, personalized messaging, and customer data platforms to give enterprises a single-provider option for all of their digital marketing needs. They’re particularly successful in their work with global consumer brands, and their past clients include Walgreens, Coach, and Volvo.

Location: Irving, TX
Founded: 1969
Price Range: $$$
Services Offered: Digital Media, Data Solutions, Customer Insights

For Technical SEO – Marketing Eye

Not all businesses need an SEO agency to write top tier content for them. If producing content is already a core part of their business model, they should look to their SEO agency to provide conversion-optimized website design, technical SEO, and strategy.

Marketing Eye offers a broad range of marketing services, but their strength is in their technical and strategic consulting. Their 15 years of experience has seen them work with clients in consumer goods, logistics, and financial services, counting Botani, Star Source Pty. Ltd., and Mint Money among their clients.

Location: Atlanta, GA
Founded: 2004
Price Range: $$
Services Offered: Marketing Automation, Marketing Consulting, Web Development

For Conversion Rate Optimization – Clay Agency

Conversion rate optimization is a difficult skill to find in an agency; while many companies mention it on their website, few treat it as an art. Because CRO is a mixture of web design, UI/UX design, and analytics, an SEO agency that is strong in this area will naturally have dedicated UI/UX and analytics experts on staff. 

Clay Agency places their focus squarely on digital strategy and UI/UX design, making them a good fit for clients whose primary SEO need is improving their conversion rate from organic visitors. Their service involves considerable online research and detailed UI/UX audits. 

Location: San Francisco, CA
Founded: 2016
Price Range: $$$
Services Offered: UI/UX Design, Product and Brand Strategy

For Voice Search Optimization – Aumcore

Voice search is the newest SEO niche, and is growing in importance as users begin to rely more and more on Siri, Alexa, and Google Assistant. This user segment is of particular importance for B2C companies, as the natural language processing technologies used in those assistants are currently optimized for everyday, non-technical speech.

Aumcore includes Voice SEO as one of their core services, and understands that keyword targeting strategies are fundamentally different for spoken and typed language. Their clients have included Comodo Cybersecurity, eviCore, and Delonghi.

Headquarters: New York, NY
Founded: 2010
Price Range: $$
Services Offered: Voice Search Optimization, Social Media, Brand Strategy

For Nonprofits & Charities – Community Boost

Nonprofits and charitable organizations can benefit just as much from SEO as for-profit businesses. The inherent trust that searchers afford to organic search results is just as—if not more—important for nonprofits, who are seeking donations from difficult-to-reach high net worth individuals and sponsors.

As this is a smaller niche, SEO companies that fall into this category are relatively rare and the largest we’ve found is Community Boost. While Community Boost offers a suite of digital marketing services, SEO is one of their core services.

Headquarters: San Diego, CA
Founded: 2012
Price Range: $$
Services Offered: Nonprofit SEO, Youtube & Display Ads, Google Ad Grant Management