Of the 27 states that have held both Democratic and Republican presidential primary elections so far, only four have had lower voting-age participation rates than Texas, where a mere 21 percent of residents 18 and older cast their ballots last month.

Arizona, Connecticut, New York and Louisiana all had turnout rates lower than Texas, according to a Texas Tribune analysis using state election results and 2015 census population estimates. In New York and Louisiana, just 17 percent of the adult populations voted in presidential primaries.

In each of those states except for Louisiana, the election was only for presidential candidates; no state or local offices were on the ballot, according to state officials. All four states use closed primary systems, meaning a person must register with a specific party before the election to be eligible to vote.

In Texas, the ballot listed presidential, statewide and local offices, and voters can decide at the polls which ballot they want; no prior party registration is required.

Factors including the weather and how decided an election already seems to be affect voter turnout each time, said Alicia Pierce, a spokeswoman for the Texas secretary of state's office.

The Texas Tribune thanks its sponsors. Become one.

“The focus of our office is not creating a number that should be, but making sure every Texan who wants to vote has the knowledge to do so,” Pierce said before acknowledging that the state “does tend to rank pretty low as far as voter turnout goes.”

The secretary of state is spending around $4 million between the primary and general elections on voter education efforts, Pierce said. This includes airing TV and radio ads as well as using social media and community outreach groups to inform voters about the Texas voting process.

"We’re trying to meet voters wherever they’re at,” Pierce said.

Despite the low turnout rate, the raw numbers looked good for Texas this year: 4.2 million people voted in this year’s primary election, the most in state history, according to the secretary of the state.

When accounting for the voting-eligible population, an estimate that excludes undocumented immigrants and felons on probation or parole, Texas jumps above Delaware and Rhode Island. On March 1, 24.7 percent of Texas' estimated voting-eligible population cast a ballot.

Thirty-five states use primary elections in both parties to hand out delegates to prospective presidential nominees. Eight of those have not yet held elections, which stretch out through June. The other 15 states and Washington, D.C., either participate in caucuses or a combination of primaries, caucuses and conventions.