Old Yeller takes place in Salt Lick, Texas, 600 miles south of Abilene, Kansas in the late 1860s. The setting is important in this novel because it is a part of a movement called "regionalism". The idea behind regionalism is that the setting is so well described that the reader cannot imagine the story taking place anywhere else. Usually, a regionalist author writes about somewhere s/he actually lived or spent time, but for this novel, the author relies on stories his parents told him about their lives some forty years prior.
The setting of a story includes time period, location, and historical context within which the action takes place. Even the atmosphere is a part of the entire frame that encompasses the tale.
As such, Old Yeller is set in the mid 1800's, specifically in 1860. The story takes place in Salt Lick, Texas and in Abilene, Kansas. Kansas, at this time, was a popular "pit stop" and one of the few places which had a terminus (one was in Abilene and another one was in Wichita), given that Texas would not have railroads until the 1880's. This is the reason why Travis's dad, as many other ranchers and farmers, had to go to Abilene to conduct business.
Also, at this time (November), Abraham Lincoln won the Electoral College, while the popular vote denoted a huge division in the nation. When Lincoln wins the presidency of the United States on his anti-slavery platform, the pro-slavery Southern states start to rebel and the first secession from the Union occurs with South Carolina being the first state to start what will become "the confederacy" in December of 1860. This is important information to truly appreciate the atmosphere of turmoil that existed within the confines of this tender and sentimental tale.
However, as of this particular novel, Fred Gipson actually focuses more on the aspects of life in Texas within the specific region where the story takes place. This gives the narrative a stronger "flavor" of the region which helps the author focus more on this particular stamp, rather than dilute the rest of the narrative with broad, historical frameworks.
The setting of Old Yeller is West Texas during the latter half of the 19th century (1800s).