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Police officers pay their respects at the funeral service for Senior Corporal Lorne Ahrens at Prestonwood Baptist Church in Plano, Texas, July 13, 2016. Stewart F. House/Getty Images

With police officers having increasingly become the target of gunfire this year, both deadly and nonfatal, some departments across the country might be concerned with their personnel dwindling as a result. Many officers have been retiring or quitting their respective forces, in part out of fear of being shot in the line of duty.

A police officer in Washington State was shot in the head while responding to a shooting in a Seattle suburb earlier this month. While that officer was recovering, 135 other officers were not as fortunate this year and died from their gunshot wounds, according to a new report from the National Law Enforcement Officers Memorial Fund released this week.

More than 12,000 municipal and city police departments in the U.S. were operating as of 2013, according to the most recent data provided by the Bureau of Justice Statistics. On average, cities with more than 50,000 residents had police forces made up of about 17 officers for every 10,000 people. The city with the greatest number of police officers is Washington, D.C. which has numerous local and federal agencies for nearly 4,000 total.

But a trend of more police officers retiring than joining the force has been picking up steam as of late, perhaps timed with the increased number of law enforcement members being shot in the line of duty. More than 100 police officers last week announced their intentions to retire from the police force in Houston, where a deputy constable was shot four times in an ambush in April.

A record number of New York Police Department officers were also considering retirement "because it’s too dangerous to stay," a local police union official told the New York Post. The same thing is happening in other major cities such as Chicago and Dallas, the latter of which had five officers killed and 12 hurt in an ambush-style shooting in July.

If the officers aren't retiring, many are just plain quitting. Nearly 100 Dallas officers resigned from the force after the July ambush shooting, and officers in Baltimore and Chicago are doing the same. Baltimore and Chicago have some of the nation's highest murder rates.