“Being counted in the census,” says David Rubenstein, the philanthropist who is also the author of “The American Story: Interviews with Master Historians,” “is the companion act of voting.”

“The People Count” traces the nation’s growth from the first census, which took 18 months and counted 3.9 million people (white landowners, their families and relatives and indentured servants). It then takes us to 1860, when nearly four million slaves were included and Native Americans were counted for the first time; 1870, when the census no longer enumerated slaves as a separate category; 1880, when, for the first time, more Americans were living beyond the boundaries of the original 13 states than within them; and 1890, when the counting was conducted with a rudimentary computer system.

“The People Count” vividly evokes the impact of race in America from the nation’s very beginning and explores why some people counted less than others.

Ever wonder why seven of the 15 presidents before Abraham Lincoln came from Virginia? Slaves were ineligible to vote, but among the many compromises — or betrayals — agreed to by the founders, the South got to count each of them as three-fifths of a white person for purposes of representation. That formula gave Southern states 47 of the 105 congressmen after 1790. By one estimate, not counting slaves at all would have given the South only 33.

“To see that the census was created in a way that counted and didn’t count African-Americans — what could make that point about more real, more stinging, more challenging?” said Louise Mirrer, the president and chief executive of the historical society.

The timely exhibition has been curated by Mazy Boroujerdi, adviser to the David M. Rubenstein Americana Collection; Michael Ryan, vice president of the New-York Historical Society; and Sue Ann Weinberg, director of the society’s Patricia D. Klingenstein Library.