"Coop"
"Coop" Cooper is second son of Lois and Tom Cooper, the eldest being Jesse. His nickname refers to his paternal grandfather.
"Coop" is portrayed by actor Liam Dickinson.
Film
Coop resides on the Coopers' farm with his family and is approximately ten-year-old when he is featured. During one of Murphy's rare visits back to the farm, she notices that Coop suffers from a chronic cough, which Coop remarks is due to the dust storms. Concerned about her nephew's health, Murph offers to bring a colleague to examine Coop, which Tom refuses. Despite Tom's refusal, Murph secretly brings her friend Getty to the farm to examine both Coop and Lois. Getty concludes that both Coop and Lois need to leave the farm immediately, given how their health will continue to deteriorate.
Before they can leave, Tom returns and angrily throws his sister and Getty out of the house. Murphy, still determined to save her nephew and sister-in-law, torches the corn fields on the farm to distract Tom while she and Getty return to the farm to evacuate her brother's family.
Novel
It is stated in the novelization, that even though his father Tom "had passed two decades ago..." "Coop" was biologically old enough to be Cooper's own father by the time he had arrived at Cooper Station. (pg. 271)
2008 script
There is no character named "Coop" in the script, however, Murph does have a daughter named Emily.