The protesters said eliminating the city force - which union officials said was 45 percent black and 35 percent Hispanic - amounted to an experiment and an assault on organized labor.
Figures from the 2010 census show that 48 percent of Camden's 77,000 residents are black.
"It is untested. It is unwarranted," said City Councilman Brian Coleman, the lone Council member to come out against the plan. "We will not allow Camden to be used as an experiment every time someone comes up with an idea."
The county force's metro division, which would patrol only Camden, is projected to have 400 officers, which would make it substantially larger than the current city department, which has nearly 260 members.
County officials have said the bigger force would be made possible because it would not be governed by current police contracts, which they term generous.
The cash-strapped city cannot afford to hire more officers and the larger force will better protect city residents, they say.
Suburban towns have balked at joining the county force.
Officials insisted Tuesday that the new force also will be racially diverse and that the NAACP was avoiding dealing with the city's real problems.
"The 'Rally for Justice' should focus on the real issue of the day, which is reducing violence in our urban centers and reducing the number of victims who fall prey to gun violence," Mayor Dana L. Redd said in a statement.
County Freeholder Director Louis Cappelli Jr. said officials were "fighting for the civil rights of ordinary citizens who are afraid to step foot outside their front door."
Camden is perennially ranked as one of the nation's most dangerous cities. Last year, the city recorded 67 homicides, its most ever.
"We are fighting for the civil rights of children in a crime-plagued city," Cappelli said in a statement.
Harris said the NAACP also believed it was "illegal" for the state Civil Service Commission to approve the city's plan to lay off the entire department, though the county has said it would consider rehiring up to 49 percent of the current city officers.
Stopping the new force "is going to be the emancipation of Camden . . . from the bossism and corruption of leaders regardless of race, regardless of gender," Harris said.
Contact Darran Simon at 856-779-3829 or firstname.lastname@example.org, or follow on Twitter @darransimon.