Correction: An earlier version of this story incorrectly reported Atlanta as having the biggest percentage decline in NLJ 250 attorneys among major U.S. cities. This year, 3,168 NLJ 250 attorneys worked in Atlanta, representing a 1.8% decline from 2009.

Chicago experienced the biggest loss this year in attorney headcounts among NLJ 250 firms in major U.S. cities.

Sliding by 6.8%, Chicago dropped 530 lawyers, for a total of 7,247 NLJ 250 attorneys this year, compared with 7,777 last year. Notable decreases occurred at Mayer Brown; K&L Gates; DLA Piper; Drinker Biddle & Reath; and Dykema.

This year’s NLJ 250, The National Law Journal‘s annual ranking of the nation’s largest law firms, showed that although Chicago and other major cities suffered sizeable losses in headcounts, there were some bright spots.

Overall, NLJ 250 firms had 1.1% fewer attorneys in 2010 than in 2009. Of 15 big cities canvassed, 12 had fewer attorneys in 2010 compared with 2009.

Among the five gainers, Houston rose by 3.8% for a total of 2,765 attorneys.

Forty-seven NLJ 250 firms have Houston offices. New York’s headcount increased by 0.4% to 21,520 attorneys. This year, 155 firms had New York offices, compared with 156 in 2009.

Houston’s increase was primarily attributable to more opportunity in the energy sector, said Joel Henning, principal of Joel Henning & Associates, a legal consultancy in Chicago. The increase in New York “corresponds to Wall Street recovery,” he said. “Wall Street bounced back and Main Street is still suffering.”

Miami also gained a bit. Its headcount grew by 1.2% to 1,278 attorneys. Los Angeles rose by 1.1%, to 5,462 attorneys.

In addition to Chicago, other cities experienced significant drops. Boston fell by 5.9% to 3,699 attorneys. Still, five more NLJ 250 firms claimed offices in Boston this year compared with last year, for a total of 50.

Washington, with 13,004 NLJ 250 attorneys, sank by 1.6% from 13,220. This year, 161 NLJ 250 firms had office in Washington, compared with 162 last year.

Seattle’s headcount fell by 2.9% to 1,046 attorneys. Minneapolis slumped by 2.4% to 1,630 lawyers; the number of NLJ 250 firms with offices there stayed steady at 18. San Francisco experienced a 1.9% slide, to 3,729 attorneys.

Other cities that lost attorneys were Atlanta, Dallas, Denver, Philadelphia and Phoenix.

Despite claims by clients that they are using local counsel for mergers and acquisitions, Henning said that many still rely on New York firms and bypass law firms in smaller cities. “They tend to lose out in the M&A environment,” he said.

Leigh Jones can be contacted at ljones@alm.com. View the full results of the NLJ 250 survey.