Fairfax County police officers used force on civilians nearly 540 times in 2015, but only one of those cases was found to have been a sustained violation of department rules, according to a new report released Monday.

The data compiled by Fairfax County police also found that more than 40 percent of use-of-force cases involved African Americans, who make up only about 8 percent of the county’s population.

Whites represented 52 percent of such cases and 63 percent of the population, while Hispanics accounted for 4 percent of such cases and are about 16 percent of the population in Fairfax County.

The first-of-its-kind accounting was released as part of an effort by Fairfax County police to be more transparent in the wake of the 2013 killing of Springfield resident John Geer by a police officer.

The case prompted scrutiny of the department and changes in its use-of-force policy. Former Fairfax County police officer Adam Torres was sentenced to one year in jail last month after pleading guilty to involuntary manslaughter.

The report found that 985 officers were involved in 539 use-of-force incidents in 2015. The most common type of force deployed was physical contact, followed by stun guns, pointed firearms and vehicle intercepts. A police officer discharged his or her firearm only one time last year.

Fairfax County Police Chief Edwin C. Roessler Jr. said the percentage of African Americans involved in use-of-force cases does not indicate that blacks are being targeted by police.

"We as a department are going where the crime is," Roessler said. "Obviously, I will not tolerate any profiling or discrimination. These calls are all generated through engagement with the community."

Roessler wrote in a message that releasing the statistics was part of an effort to improve transparency in "all areas" and increase the public's confidence in the police department.

In about 98 percent of the use-of-force cases, the report found that the civilians who were involved were unarmed.

African Americans also represented a significantly higher number of the field stops by police in relation to their numbers among the overall county population. About a quarter of field stops involved African Americans, while 66 percent involved whites and 2 percent involved Hispanics.

The number of cases of use of force on people suspected of being mentally ill edged up from 36 in 2011 to 44 in 2015, according to the report. During the same period, the number of calls to police to respond to people who were having mental health crises increased from more than 2,200 to more than 2,800.

Fairfax County's chapter of the NAACP did not immediately return calls for comment about the findings on Monday evening.