Photo: John Davenport, Staff / San Antonio Express-News Photo: File, Houston Chronicle Photo: Ana Isabel Photography/ J. Scott Applewhite, STF / Associated Press Photo: Elizabeth Pudwill / Jeremy Carter / HC Photo: Washingtonpost/Tom Williams / Contributor

The Texas voter rolls have grown to 15.6 million people, a new record, and a jump of 1.6 million since the last time Texas held a midterm election in 2014, said Texas Secretary of State Rolando Pablos.

That includes nearly a 400,000-person increase since March, election records show. To put that number in perspective, from 2002 to 2014, the state added just over 100,000 voters a year, on average.

Since March, the state’s largest counties, Bexar, Harris, Dallas and Tarrant, all saw their voter registrations grow about 2.4 percent on average.

“Recently, we have heard from a number of county election officials who tell us they are witnessing voter registration rates and voter enthusiasm in a midterm year that we usually see before Presidential-year elections, which is phenomenal,” Pablos said. “On the whole, we are seeing Texans become more engaged, which is very healthy for the future of our state.”

The surge of registered voters comes as Texas watches the hottest U.S. Senate race in the country between U.S. Sen. Ted Cruz and Democratic Congressman Beto O’Rourke, as well as a half-dozen close congressional races that could determine control of the U.S. House of Representatives.

More Information Voter Registration in Texas For Midterm elections over last 20 years 2018 - 15.6 million 2014 - 14.0 million 2010 - 13.2 million 2006 - 13.1 million 2002 - 12.6 million 1998 - 11.5 million SOURCE: Texas Secretary of State

Over the past six months, Harris County has added 55,000 voters — more than any other county. But the growth has been even more pronounced in suburban counties ringing Houston. In Fort Bend and Montgomery counties, voter rolls grew 3 percent. In Collin and Denton counties just north of the Dallas-Fort Worth metroplex, voter registration jumped almost 4 percent.

Two fast-growing counties that border Austin have seen the largest gains by percentage. In Williamson County, just north of Austin, the voter registration jumped over 4 percent. The biggest gain since March has been in Hays County, which saw a 4.4 percent increase in the number of registered voters.

The burst in interest from voters is evident in counties with competitive races for Congress, adding an extra degree of uncertainty to those races. The 22nd Congressional District, which includes most of Fort Bend County, the 32nd Congressional District, which includes Collin County, the 21st District, which includes parts of Hays County, and the 31st District, which includes Williamson County, are considered the races with Republicans facing some of their stiffest opposition in Texas.

The jump in registrations in those districts make sense, University of Houston political scientist Brandon Rottinghaus said.

“Competitive elections increase voter interest,” he said, adding that the U.S. Senate race is also a factor.

And there is still time for more voters to join the rolls before Oct. 9, the final day to register in time to vote in the midterm elections.

The surge in voter registration comes despite the difficulties of registering voters in Texas. State law requires that to register voters, a person must be trained by a Volunteer Deputy Registrar in each county they do their work, a provision that discourages many groups from doing voter registration drives.

To register to vote, Texas residents can fill out an application online or contact their county election administrator’s office.

Registering to vote and casting a ballot are two different things in Texas. Despite having 14 million registered voters in 2014, just 4.7 million people voted — about 34 percent of voters. In presidential cycles, voter turnout is much higher, hitting almost 60 percent in 2016 and 2012.

jeremy.wallace@chron.com