From University of California, Los Angeles (UCLA) webpage for Professor Leonard Kleinrock, The Day the Infant Internet Uttered its First Words:

“Below is a record of the first message ever sent over the ARPANET. It took place at 22:30 hours on October 29, 1969. This record is an excerpt from the "IMP Log" that was kept at UCLA. Professor Kleinrock was supervising his student/programmer Charley Kline (CSK) and they set up a message transmission to go from the UCLA SDS Sigma 7 Host computer to another programmer, Bill Duvall, at the SRI [Stanford Research Institute] SDS 940 Host computer. The transmission itself was simply to "login" to SRI from UCLA. They succeeded in transmitting the "l" and the "o" and then the system crashed! Hence, the first message on the Internet was "lo", as in "lo and behold! They were able to do the full login about an hour later.”

From the Newsroom:

From Census.gov > Topics > Population > Computer and Internet Use:

Source: 2018 American Community Survey, 1-Year Estimates.

From 2020 Census:

Note: The 2020 Census marks the first time you'll have the option to respond online. You can even respond on your mobile device.

From the Library > America Counts: Stories Behind the Numbers: