Robert Sarvis, a Libertarian candidate for the U.S. Senate, wants to open the nation’s borders.

"Did you know US population growth is at its lowest since the Great Depression?" he tweeted on April 1. "RT if you support liberalizing our immigration laws."

"RT," if you’re wondering, means retweet. That cleared up, we didn’t know that the nation’s population growth had reached an 80-year low.

So we decided to look at data from Sarvis’ primary source: the U.S. Census Bureau. We found mid-year population estimates dating back to 1900.

The lowest point was from mid 1917 to mid 1918, when the U.S. began sending troops to Europe for World War I and the nation’s population actually decreased by 60,000, or 0.06 percent. That’s the only time since the start of the last century when the number of people decreased.

Save that year, population growth hovered between 1 and 2 percent until 1931 when, in the teeth of the Great Depression, it dropped to 0.78 percent. It bottomed at 0.59 percent during the 12-month period beginning in July 1933. U.S. Population growth did not climb above 0.8 percent until mid 1939.

From there U.S. population growth increased gradually through the ‘40s, peaking at 2.05 percent in 1950, and staying above 1 percent until 1973. It generally hovered at slightly below 1 percent through 2009.

In 2010, as the nation was slowly emerging from recession, the growth rate plummeted to 0.84 percent, followed by 0.72 in 2011, 0.74 in 2012 and 0.72 in 2013.

Indeed, the last four years mark the four lowest points of population growth since the Great Depression. And the growth rates of 2011 and 2013 are at the bottom of the time span.

William Frey, a demographer at the Brookings Institute, says U.S. population growth is closely tied to the economy. During bad times, couples delay having children.

In 2012, only 12.6 percent of U.S. women aged 15-44 had children, according to data compiled by the Centers for Disease Control and Prevention. That’s the lowest birth rate in records dating back to 1940. Women in that age group had 3.95 million babies in 2012, a drop of 368,000 births from five years earlier.

Immigration has slowed since the start of this century, but has been rebounding in recent years. In 2001, there was a net increase of nearly 1.2 million immigrants in the U.S. and that dropped to 726,000 in 2009. Last year, there was a net increase of 843,000 foreigners.

Our ruling

Sarvis said the U.S. population growth is at its lowest level since the Great Depression. The figures back him up and we rate his statement True.