A sign on the Colville Reservation in Washington. Photo from Department of Transportation

The U.S. Census Bureau will conduct test counts on two reservations next year.

The counts will reach about 3,500 housing units on the Colville Reservation in Washington, according to the agency. Another 2,900 units on the Standing Rock Sioux Reservation in North Dakota and South Dakota will be included.

"The 2017 Census Test will allow the Census Bureau to test the feasibility of collecting tribal enrollment information. It will also refine our methods for enumerating areas with unique location characteristics, where we cannot mail to a street address," the agency said in a press release. "In addition to tribal areas, the test will oversample areas with relatively high populations of American Indians and Alaska Natives as a mechanism for testing potential tribal enrollment questions nationwide."

The tests come in preparation for the 2020 Census. The federal government conducts a count every 10 years and the figures are important because they help determine funding levels and Congressional representation.

Historically, American Indians and Alaska Natives living on reservations and in rural areas have been undercounted. The rate was 4.9 percent in 2010, about the same as the 4.74 percent undercount in 2000, but a marked improvement from the 12.2 percent undercount in 1990.

According to the agency, 5.2 million people identified as American Indian or Alaska Native on the 2010 Census.