Not much is known about the origins of Hold 'em and what is known has very little evidence to back it. There is no specific information pertaining to where or when the first game was played, however, the earliest game is said to have been played in the early 1900's in Robstown, Texas. The first time it appeared in Dallas, Texas was in 1925.
The game was later brought to Las Vegas by a number of Texan gamblers. A few members of this group were Crandell Addington, Doyle Brunson, and Amarillo Slim. Picking up speed, the game finally reached popularity in 1970. In the same year the Horseshoe Hotel and Casino was opened in Las Vegas by a man named Benny Binion and the first World Series of Poker tournament was played in it and has been held annually ever since.
In present day, Texas Hold 'Em is well known all across the world and can be played everywhere not just in casinos but also at home and is even available on the internet and on cellphones.
Source: thepokerfather.com