BOSTON (AP) – If you live in the Boston area, you may already know that some of your neighbors are wealthy. But over the next five years, the number of millionaires in the region is expected to increase by 50 percent, according to two wealth management companies.

The Boston metropolitan area already has a high percentage of millionaires in its population – 4.8 percent, or nearly one in 20 households – a higher percentage than in New York, Chicago and Los Angeles, each with 3.7 percent of its population as millionaires.

By 2009, the number of millionaire households in the Boston region is expected to jump to 88,000, up from 58,000 in 2004.

The projected increase in millionaires will be fueled by several factors, according to William Whitt, vice president of strategic marketing at Northern Trust, which obtained information on the growth in millionaires from Claritas Inc., a demographic data company.

Some of Boston’s principal industries, including technology companies, law firms and financial services companies, pay their executives high salaries.

Also, a generation of baby boomers is entering peak earning years and saving for retirement in 401(k) plans, so that even middle managers can save more than $1 million.

Economic growth is also expected to contribute to the increase. The Northern Trust data defines millionaires based on a person’s liquid investable assets, which includes retirement assets, bank accounts, stocks and bonds, but does not include homes.

“You have a lot of wealth created through regular retirement savings plans,” Whitt said. “The upper middle management has managed to save quite a bit of money.”

In the Boston area, millionaires are found mostly in suburban towns, according to the Claritas data. In Lincoln and Weston, more than a quarter of the households are millionaires. The 02110 zip code of downtown Boston has 24 percent millionaires.

For companies that serve the wealthy, business is booming.

Steakhouse Smith & Wollensky, where the average diner spends about $72 on dinner, opened in Boston’s Back Bay neighborhood in 2004. Business has been so good that the restaurant opened for lunch, and executives have said they expect Boston to outperform most other locations in the next 10 years.

AP-ES-01-01-06 1204EST