The first national census took place on August 2, 1790, when marshals under the direction of Secretary of State Thomas Jefferson canvased the original 13 states plus Maine, Vermont, Kentucky, and the Southwest Territory (Tennessee). They asked six questions: name of the head of the household, and number of persons in each household in these categories: free white males over 16; free white males under 16; free white females; all other free persons; and slaves.

A total of 3,929,214 were counted. Compare that to 2010, when the count was 308,745,538. In what would become a decennial dissatisfaction, not everyone was happy with that very first count; both President George Washington and Secretary Jefferson expressed skepticism about the total, believing it was too low.

As Kenneth Prewitt reminds us, the census is mandated by the Constitution. It has always been political: as he explains, the Constitution replaced a weak confederacy with a strong national government. One of the compromises for the smaller states was a bicameral national legislature. Every state would get two Senators, and so be equal in the upper house, while the House of Representatives would be “proportionate to population.” That meant there had to be a head count.

Since the U.S. was continuing to expand, this survey had to be done regularly, every ten years. Prewitt argues that the census’s purpose is “reallocation of power as the population grows and regulating the expansion of the union.”

After the census, a reapportionment of representatives (and hence electoral votes) takes place. Since the census numbers set the stage for a decade or more of politics, it’s not surprising the results have been fought over since the beginning. In a particularly egregious case, Southern Congressmen did not want to dilute their power after the first wave of the Great Migration (1916-1930) shifted more than a million African Americans to the north, so they simply blocked reapportionment after the 1920 census. The next House apportionment wouldn’t happen until after the 1930 count.

It isn’t just House seats that are apportioned based on the census. Federal funding to the states is also based on population. And as Prewitt details, it’s no longer just the results of the census that are contested. Since the 1980, the means of the census have become the subject of lawsuits and partisan conflict. The biggest contention is how to account for the “undercount,” a statistical given in such a large survey.

Typically, few think about the census during the years between them—the next is 2020—yet the counts remain fundamental to our political system. So…happy birthday, problematic national census!