Pakistan led the list of fatalities with eight, followed by Iraq with four and three each in Honduras and Mexico, the New York-based CPJ said.
The total number of reporters killed in connection with their profession was much lower than in 2009, when the record figure of 72 worldwide was skewed by a one-off massacre in the Philippines.
In addition to the 42 known to have been killed this year, another 28 journalists died in still unclear circumstances, the CPJ said.
“The killing of 42 journalists in 2010, while a decline over previous years, is still unacceptably high and reflective of the pervasive violence journalists confront around the world,” said CPJ executive director Joel Simon.
“From Afghanistan to Mexico, Thailand to Russia, the failure of governments to investigate crimes against the press contributes to a climate of impunity that ultimately fuels further violence.”
Most of the 42 deaths were murders, while 40 percent took place in combat and other dangerous circumstances.
“Suicide bombings and crossfire in Pakistan, Afghanistan, Thailand, and Somalia accounted for the unusually high proportion,” the CPJ said.
Nearly all the victims were local reporters. Six of them were Internet-based journalists.
“CPJ research shows that about 90 percent of journalist murders go unsolved despite the fact that many victims — 60 percent in 2010 — reported receiving threats in the weeks before they were killed,” the rights group said in a statement.