The officer was identified as Detective Alejandro "Alex" Cervantes of the Euless Police Department.
One injured adult was in critical condition at John Peter Smith Hospital while two children were being treated for serious injuries at Cook Children’s Medical Center, the Fort Worth Star-Telegram reported.
The family was traveling at Boat Club Road and Rocky Point Trail in Lake Worth, northwest of Fort Worth, in a Chevy Impala around 3 p.m. when their vehicle was struck by a Jeep Wrangler, Euless police said in a statement.
The Wrangler driver was identified as Dylan Molina, 26, of Lake Worth. He was expected to be charged with intoxication manslaughter and three counts of aggravated assault, authorities said.
Molina's vehicle allegedly ran a red light prior to the crash, and witnesses claimed he tried to flee on foot afterward, the Euless police statement said.
The suspect had allegedly been drinking at a tavern in Lake Worth prior to the crash, FOX 4 reporter David Sentendrey disclosed in a Twitter message.
Molina was allegedly speeding while driving home when he struck the off-duty officer’s car, Sentendrey reported.
Cervantes served with the Euless Police Department for more than six years and previously served with the El Paso Police Department, the Euless police statement said.
"Please keep Alex's family, friends, colleagues, and the Euless community in your thoughts and prayers during this extremely difficult time," the statement requested.
Euless is about 20 miles west of downtown Dallas.
Lake Worth police and personnel from other law enforcement agencies responded to the scene, according to the Star-Telegram.
More information about the crash will be released after family members are notified, Lake Worth police Chief J.T. Manoushagian told the Star-Telegram.