State officials said Monday that about 60 percent of those users were signing up to vote, while the rest were changing their name, address or party affiliation.
Democratic Gov. Tom Wolf, who launched the system in August 2015, says the results reflect demand for election systems that are more secure, easier to navigate and help ensure that votes count.
Elections officials say online registration has reduced the workload and cost for county elections officials, who can be flooded with applications near registration deadlines.
Voters have until April 16 to register if they want to participate in the May 15 primary.