Prisoners count. But where?

That's a question state lawmakers across the country are grappling with as the 2020 census approaches.

Last week, Washington Gov. Jay Inslee, a 2020 Democratic presidential candidate, signed a bill to make his state the latest to require that prisoners be counted at their pre-incarceration addresses — instead of where they're serving time — to end the practice of what critics call "prison gerrymandering."

That's important, advocates say, because the Census Bureau currently counts prisoners as residents of the locations where they're imprisoned, and states use the census data to draw their legislative maps.

While a significant number of correctional facilities are located in comparatively rural areas that are largely Republican and predominantly white, prisoners tend to hail from urban, often Democratic communities and are disproportionately minorities, criminal justice experts told NBC News.

Advocates of change, including many Democrats, say it's unfair to count prisoners as residents of communities whose demographic makeup and needs differ from the places the inmates call home. They argue that inflating the power of residents in districts with prisons violates the constitutional principle of one person, one vote.

But supporters of the status quo, including many Republicans, say prisoners should be counted where they're incarcerated, both because of longstanding tradition and because communities where prisons are located need to receive adequate funding for the services they provide. They characterize efforts to overhaul the counting method as a partisan move that would largely benefit Democrats.

The laws that have been enacted in Washington and other states focus solely on adjusting population counts for redistricting and leave funding calculations unchanged.

Picture two legislative districts side by side — one with a large prison and one without such a facility. Each sends one state senator to represent its constituents at the statehouse. Districts are required to have roughly equal population sizes, but due to prison gerrymandering, the prisoners are counted as part of the population of the district with the correctional facility. That means the non-incarcerated residents of the district with the prison, even though they are fewer in number than those who live in the neighboring district, enjoy more voting power than residents in the district next door without a prison.

The sponsor of the bill in Washington, Democratic state Sen. Jeannie Darneille, said addressing the legislative redistricting issue is a question of fairness.

African Americans and other minorities have been unjustly undercounted since the census began, Darneille said. "Counting of inmates at the facilities where they are detained is a continuation of this tragic tradition, especially in the era of mass incarceration," she added.

Since the first census in 1790, the Census Bureau has counted people based on the concept of "usual residence," defined as the place where they live and sleep most of the time, which for prisoners means where they're incarcerated.

Oliver Hinds, a senior data scientist at the Vera Institute of Justice, said that counting method can distort estimates of legislative district populations. While a significant number of prisons are located in rural areas, he added, "our best estimates" indicate that only 15 percent of the prison population comes from such areas.

In setting its rules for the upcoming census, the Census Bureau received almost 78,000 comments on how prisoners are counted, including from former heads of the agency, civil rights groups and elected officials — almost all of whom urged the bureau to tally prisoners at their home addresses.

The bureau, however, decided not to change its method of counting prisoners, although states like Washington have passed laws requiring for adjustments to the census population counts during legislative redistricting.

Efforts to address the issue at the federal level have gone nowhere. Rep. Mark Pocan, D-Wis., included an amendment to end prison gerrymandering in a sweeping overhaul of voting, campaign finance and ethics laws that passed the House in March, although the bill will not advance in the Republican-controlled Senate.

Absent federal action, New York, Maryland, Delaware and California have passed measures like Washington's, and several other states are considering similar legislation.

In New Jersey, a bill to end prison gerrymandering passed the Democratic-controlled Senate by a largely party-line vote in February but has not been taken up by the Democrat-led General Assembly.

"This bill will ensure the voices in our communities are not diminished because their residents are serving time," Democratic Sen. Nilsa Cruz-Perez, a sponsor of the bill, said. She represents a district that includes Camden.

The only Republican to vote for the measure, state Senate Minority Whip Joseph Pennacchio, said it seemed "unnatural" to count prisoners where they're incarcerated given that they're likely to return to their previous communities upon their release.

In vetoing an earlier bill to address the issue, then-Republican Gov. Chris Christie echoed others opposed to changes, saying the measure ran counter to the Census Bureau's longstanding practice, and claiming it made "little sense insofar as prisoners are consuming services and resources at the prison and may have only fleeting, dated, or tenuous ties to their prior residence."

In Connecticut, the NAACP filed a lawsuit last year to end prison gerrymandering after several attempts to address the issue legislatively over the last decade failed.

The lawsuit comes amid several others charging partisan or racial gerrymandering around the nation, including cases that are currently before the Supreme Court. It asserts that counting inmates at their prison addresses has distorted populations in several legislative districts, raising constitutional concerns.

The president of the NAACP's Connecticut chapter, Scot Esdaile, said he thinks it's unfair that two state senators have the same amount of legislative power despite one representing a district without a prison and another representing a district with a prison in which all the inmates are counted as residents of that district even though all or most never resided there or even voted in the district.

"It's a farce, smoke and mirrors," Esdaile said, adding that lawmakers who are blocking change "should be ashamed of themselves of how they’re robbing the people for political gain.”

In Illinois, where Democrats also control both chambers of the state Legislature, state Democratic Rep. La Shawn Ford has reintroduced a bill to end the practice.

"There's no reason to take away individuals' right to be counted in their home territory," he said.