CNN Declassified, "Spies among us: Get a peek at their playbook" by Thom Patterson, Updated July 18, 2017, reports of an expert estimate of 100,000 foreign agents:
(CNN)Spies are living among us.
In the United States alone, one expert estimates that there are about 100,000 foreign agents working for at least 60 to 80 nations -- all spying on America.
"That's not paranoia -- that's a good guess," said Chris Simmons, a retired counterintelligence supervisor for the U.S. Defense Intelligence Agency, appearing on CNN's "Declassified."
On page 60 of the Feb 18 - March 3, 2019 TV Guide magazine, a half page write-up of NBC's thriller The Enemy Within begins with the sentence:
Let this chilling fact sink in: An estimated 100,000 foreign spies reside in the U.S. working to undermine America every day.
This vague factoid brings up various related questions:
- Are 100,000 foreign agents (CNN) the same thing as 100,000 spies (TVG)?
- Whose estimate is this? (TV Guide doesn't say, presumably it's the Chris Simmons estimate)
- How was this estimate arrived at?
But the main question would be: approximately how many foreign spies are in the US?
Presumably that's impossible to know, though it might be publicly knowable over the decades when historians get to survey eventually declassified documents, but a brief survey of present-day "spy census" estimates and the ranges of numbers they offer would better than nothing.