GET READY TO ENUMERATE: The decennial census, the government's single largest civilian undertaking, wants to find everyone this time.

• Author: Potyondy, Patrick
• Position: THE CENSUS

The U.S. Constitution requires an "actual enumeration," or counting, every 10 years of every person in the country. In the first count, in 1790, 17 marshals and their assistants were given nine months to complete the job.

The marshals faced several hurdles, not least because it was the first count. Roads were often impassable, if they existed at all. Bridges were scarce, forests impenetrable, people suspicious, and the horse was the only mode of transportation. It took the marshals twice their allotted nine months, but they came back with a final count: 3,929,214 people living in 13 states.

They counted the heads of households, the number of free white males 16 and older (for purposes of war), free white males under 16, free white females (but not their age because it was thought to be "indelicate... to ask a young lady"), other free persons and slaves. After considerable debate, Congress decided against lames Madison's proposal to collect detailed data on Americans' occupations, citing the expense and potential unconstitutionality.

George Washington and Thomas Jefferson suspected, but had no way of proving, that the 1790 enumeration greatly undercounted certain groups and families. Indeed, an undercount was intentional back then. Only three of every five slaves were counted, and Native Americans weren't counted at all. That didn't change until after the Civil War and the passage of the 14th Amendment, when the country began counting the "whole number of persons" in each state.

It's Coming Again

Our next counting begins around April 1, 2020, and the stakes could hardly be higher: The census is the basis for congressional apportionment (how many seats each state gets); redistricting at all levels of government (how we draw the lines for the U.S. House of Representatives, state legislatures and school boards); decision-making by public officials, businesses and nonprofits; and the annual allocation of more man $800 billion in federal funding to the states.

Missing less than 5 percent of the population might seem unimportant given the size of the country, but even a 1 percent undercount could cost a state a U.S. House seat and millions of dollars in federal funding.

Transportation and communication have improved greatly since 1790, but the dedicated public servants of the U.S. Census Bureau still wrestle with the question of how to reach everyone in the country and avoid an undercount. As lawmakers consider ways to ensure that every person in...