CBP published the figures as it issued new guidelines formalizing the way its officers conduct searches and handle the information they obtain.
The agency said the increase was not the result of a policy directive, but rather an indication that electronic devices are increasingly viewed as critical sources of information on potential security threats.
"In this digital age, border searches of electronic devices are essential to enforcing the law at the U.S. border and to protecting the American people," CBP official John Wagner said in a statement.
American citizens and other travelers have expressed astonishment and alarm in recent years at requests to hand over their cellphones from U.S. customs officials at airports and border crossings.
But CBP said the practice is justified and its standards have been thoroughly reviewed to ensure they are not an unreasonable violation of privacy rights.
The agency said it sometimes needs information it obtains from devices to determine the admissibility of foreign visitors, viewing them as potential sources of intelligence on terrorism, child pornography or other criminal activity.
Under the new guidelines, travelers who are selected by its officers for additional screening could be asked to unlock their electronic devices for inspection or provide passcodes. They will be asked to disable the devices' data transmission, according to a senior CBP official who briefed reporters on the changes Friday.
Only information physically stored on the device — such as photographs or phone numbers — would be subject to search, said the official, who the agency would not allow to be quoted by name. CBP agents would not be allowed to seek information stored externally or on a "cloud" linked to the device.
Such inspections would constitute a "basic search," the agency said. But in cases where officers determine they have reasonable suspicion of a criminal act or potential threat to national security, they may, with a supervisors' authorization, conduct an "advanced search" by connecting it to other applications and potentially copying its information.
Passwords provided by travelers would be destroyed and not retained by the government, the CBP official said.
Sen. Ron Wyden (D-Ore.), a key ally of privacy rights groups, called the new CBP guidelines "an improvement" but said they're still too intrusive for U.S. citizens.
"Manually examining an individuals' private photos, messages and browsing history is still extremely invasive, and should require a warrant," he said in a statement. "I continue to believe Americans are entitled to their full constitutional rights, no matter where they are in the United States."
Last year U.S. civil rights groups filed suit against the federal government in an attempt to curb device searches.
According to the senior CBP official, about 20 percent of the travelers whose devices are inspected are U.S. citizens. The rest are permanent residents, visitors or other travelers whose admissibility to the United States is subject to CBP discretion.
In cases where noncitizens refuse the search, they could be denied entry and sent home.
CBP said the decision to review a travelers' electronic device would not be made at random, and would be requested by officers as part of their broader effort to evaluate whether to allow someone into the U.S.
Imagery and information that is noncriminal, including political or sexual content, could also be used by CBP officers to determine whether to admit a foreign visitor, the CBP official said.