Truxton Trust has just one office, in Nashville, but it boasts clients in some of the wealthiest locales in the country, including Silicon Valley and New York.

The $405 million-asset Truxton, which specializes in wealth management, has come by those clients by tapping existing customers for referrals. While it hardly ignores the Nashville market, which has a fair amount of wealth in its own right, Truxton has built itself into a fee-generating machine in part by giving its advisers the freedom to travel to far-flung markets to serve affluent customers.

"We would contend that a branch network is not necessary," said Derrick Jones, senior managing director and head of wealth management. "You have to be in front of the client, but you don't have to have a physical presence to accomplish that."

This approach to acquiring customers is just one strategy banks are employing to attract more wealthy customers. Others are choosing to stay closer to their home markets or are teaming up with robo-advisers, but all have the same goals: to generate more fee income at a time when margins from lending continue to shrink.

Attracting millennials is particularly important to this mission. Though most have not yet reached their full earning potential, millennials are highly educated and financially savvy. They also stand to inherit unprecedented wealth, as more than $30 trillion of assets is expected to change hands from baby boomers to children and grandchildren over the next 40 years, according to various estimates.

The $16 billion-asset Arvest Bank in Fayetteville, Ark., is one of those banks that prefers to target affluent customers in its existing markets. However, it has only about 80 licensed brokers serving about 250 branches, so it recently began a program to train non-certified bankers in basic wealth management concepts, said Jim King, the president of Arvest Wealth Management.

"The non-broker associate can have the low-level discussions, trying to make Arvest customers more aware of what we offer," said King, whose group manages about $9.3 billion of client assets. "If the customer needs more financial advice, they would refer that to a fully licensed broker."

The $29 billion-asset Synovus Financial in Columbus, Ga., is aiming to attract wealthy client by hiring more private bankers in more affluent markets in its footprint, including Tampa and Jacksonville, Fla.; Birmingham, Ala. Nashville and Chattanooga, Tenn., said spokesman Lee Underwood.

Truxton, by contrast has clients in roughly 20 states where it has no branch presence. Many are in markets where there are high percentages of affluent millennials, including places like San Francisco, Washington, D.C., and New York.

The approach has paid off handsomely for the 12-year-old Truxton, which last year generated more than 40% of its revenues through fees, according to Federal Deposit Insurance Corp. data. Its ratio of fee income to assets in 2015 was 2.22%, or roughly three times the average for community banks with less than $2 billion of assets, according to data compiled for American Banker by Capital Performance Group.

"We live in a mobile society and families are scattered," said Jones, its head of wealth management.

California is home to three of the 10 metropolitan markets in the country with highest percentages of affluent millennials. Silicon Valley is No. 1, San Francisco/Oakland ranks No. 2 and Santa Cruz is ranked No.9, according to data from Equifax/IXI Services.

Rounding out the top 10 are Ithaca, N.Y., New York City, Washington, Boston, Boulder, Colo., Seattle and Oxford, Miss.

Isio Nelson, lead executive for the IXI Services division of Equifax, said that branches remain the primary vehicle for making contact with affluent prospects.

But, he said, even if a bank can't open a branch in Manhattan or across the street from the White House, it's important to know where wealthy millennials and baby boomers live.

"The information can be used for targeted advertising," he said. "When an institution can better understand the composition of markets, it enables them to ensure the right financial advisers are tied to the right territories."