The city’s 1st Precinct, which includes the Financial District and ground zero, had the largest crime drop in Manhattan this year, and the concentration of counterterrorism police in the area could be a factor.

Crime dropped 10.9 % at the 1st Precinct through December 5, largely because of declines in felony assault, burglary, and grand larceny, according to Compstat, a system used by the police department to track the seven major FBI crime categories. The crime decline for Manhattan’s southernmost precinct was more than double the citywide drop of 4.8%.

“It shows that Lower Manhattan is a very safe place and getting safer all the time,” Council Member Alan Gerson said. “The greater and more intense concentration of security personnel is clearly having a beneficial effect in terms of crime. Beyond the normal police department, we still have a greater number of security personnel throughout the district.”

The decline in crime was led by a 40.7 % drop in burglaries, to 218 from 368, a 6.1% decline in grand larcenies, to 1,548 from 1,650, and a 11.2% slide in felony assaults, to 111 from 125.

A police spokesman, Paul Browne, attributed the decline to good policing. “It demonstrates continued intense focus on conditions, from quality of life to violent crime,” he said.

Mr. Gerson, a Democrat whose district includes the 1st Precinct and parts of four other precincts, said the ramped-up police presence in Lower Manhattan, which was bolstered by counterterrorism police following the attacks of September 11, 2001, contributed to the fall in crime.

Following the attacks, some 5,000 officers from the 35,500-member police department were deployed to counterterrorism duties, including the guarding of bridges, tunnels, historical sites, and financial facilities. The 1st Precinct is filled with potential terrorist targets, including the Brooklyn Battery Tunnel, the Holland Tunnel, the New York Stock Exchange, City Hall, and Federal Hall.

The 1st Precinct has been attacked by terrorists on four occasions, including the 1993 and 2001 attacks on the World Trade Center, the 1975 bombing of Fraunces Tavern, and the 1920 bombing outside the offices of J.P. Morgan & Co. Police now maintain a round-the-clock watch at potential terrorist targets.

The 1st Precinct experienced a reduction in every crime category except murder and grand larceny auto. So far this year, there have been two killings in the 1st Precinct, a tally unchanged from last year. Car thefts increased 7.2%, to 119, this year from 111 during the same period last year. In comparison, homicide slipped 3.6% citywide and grand larceny auto fell 11.6%.

However, these declines in felonies fail to reflect the problem of “livability offenses,” such as noise and parking violations and illegal vending, Mr. Gerson said.

Eardrums are assaulted by a near constant barrage of noise from motorcycles, nightspots, and construction equipment, while sidewalks are clogged by illicit vendors with their tables full of wares, and “terrible” traffic congestion results in illegal parking “all over the place,” Mr. Gerson said.