U.S. Sen. Lindsey Graham joked at a CNN town hall last week that he had "never met an illegal Canadian."

Graham made the comments on Mar. 1, at a town hall with U.S. Senator John McCain. The pair had been asked about immigration to the U.S., and how they felt about families being separated by President Donald Trump's position on immigration reform.

"Have you ever wondered why we're not being overrun by illegal Canadians? We got two borders, one with Canada, one with Mexico. I've never met an illegal Canadian. They may be out there. I'll go look for them," Graham said, according to a CNN transcript of the event.

"People come in from poor countries to work here. They come to Myrtle Beach, Canadians do. They enjoy themselves, they go swimming in March, and they go home. We're glad to have them. Nobody else swims in March," he continued.

"We got two borders, one with Canada, one with Mexico. I've never met an illegal Canadian. "

It's relatively easy for Canadians to visit the U.S., which is one reason there might be many more "illegal Canadians" in the country than Graham thinks.

The U.S. is cracking down on illegal immigration from Mexico, and the Department of Homeland Security's (DHS) Customs and Border Protection agency has asked companies to submit proposals to build a wall along the country's southern border. Trump has also signed an executive order that bans travel from six Muslim-majority nations, and suspends the country's refugee program indefinitely.

But Canadians with a passport can enter the U.S. without a visa, and can stay for up to six months at a time.

In 2012, approximately 801,000 Canadians were living in the U.S., most of them legally, according to the Migration Policy Institute.

DHS released a report on visa overstays in 2015. Out of 527,000 foreign nationals who overstayed their visas (which were issued either for business or pleasure), 93,000 were Canadian and 42,000 were Mexican.

The number released by DHS may not capture the full picture. It doesn't account for Canadians who left the country via land border crossings, or those who came to the U.S. without a visa and stayed longer than six months. Pew Research estimated that out of 11 million unauthorized immigrants living in the U.S. in 2014, 100,000 were Canadian.

Canadian immigrants may also be less visible than immigrants from other countries. Most of them speak English, have health insurance and experience a lower poverty rate than immigrants from other countries, according to the Migration Policy Institute.

"It’s not as though they are not there, but they would be a little difficult to pick out, even if you were trying," demographer Bob Warren told Politifact.

However, with new crackdowns at the U.S. border, some Canadian travellers are suddenly facing more scrutiny.

A Canadian doctor who also carried an Afghanistan passport was questioned for hours at the border before being let into the country, according to The Guardian. A Muslim Canadian was denied entry after being interrogated about her religion.

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