The Pentagon is sending 3,750 additional troops to the border for three months to support border agents.
The deployment will raise the total number of active-duty forces supporting Customs and Border Protection agents there to about 4,350.
The Pentagon disclosed the official figure days after a Democratic lawmaker said about 3,500 extra troops would be deployed.
President Trump is expected to talk about immigration and his proposal for a wall along the during the annual State of the Union address on Tuesday.
Trump’s demand that money for the wall be included in spending legislation prompted a 35-day partial federal government shutdown that ended on Jan. 25.
If lawmakers cannot reach a deal on the border security situation by Feb. 15, Trump has threatened to let the government shut down again or to declare a national emergency as a way to get the money needed.