Since The Things They Carried is about the Vietnam War, the principal geographic setting is Vietnam, out in the bush (what the soldiers often call the "boonies"). The reader is introduced to this setting in the first and titular story of the collection, in which the men march "up the hills and through the swamps." In some of the other stories, the narration slows down, as the narrator focuses more on moments in which the soldiers remain still in a single setting, like at foxholes or on listening operations.
At multiple points throughout the collection, the forests, mountains, and rivers have such a dominating presence that they almost seem to be characters. The collection contains a number of specific place names, such as Than Khe, Chu Lai, Danang, My Khe, Song Tra Bong, and Quang Ngai City. The narrator also mentions that they go to Australia for R&R and are taken to Japan for hospitalizations, but none of the stories actually feature these places as settings.
At the same time, "The Things They Carried" immediately introduces the reader to the fluctuation of the setting. Even in moments when the soldiers firmly find themselves in Vietnam, the narrator brings the reader into their flashbacks to life before the war—along the Jersey Shore, in Oklahoma City, and so on. The men's high school or college sweethearts become symbols of normalcy and their hometowns, and they take comfort by reading letters or looking at photographs. Either by way of memories or letter-writing, the young men dream themselves closer to home.
Additionally, the collection's actual setting shifts between the years before, during, and after the war. This can be seen by running through the settings of the first few stories. While the first story is set in Vietnam during the war, the second story is set in the U.S. many years after the war has ended. The third story is set all over Vietnam, but the gap between the events and their narration feels much greater than in the first story. Part of the reason "Spin" seems extra retrospective is that O'Brien fast-forwards to the 1990s, his time of writing, and expresses guilt for being "forty-three years old" and "still writing war stories." The fourth story is set in the US, but recounts a period of O'Brien's life before the war—between receiving his draft letter and going to Vietnam.
Because O'Brien is an honest and self-reflexive narrator, many of the stories contain both his voice as a young soldier and his voice as an older adult. The narrator's distance from the events he recounts, and thereby the dominant temporal setting, varies from story to story. Paying attention to tense can give the reader useful hints about the temporal layer of a given moment. Although the stories are mostly written in the past tense, O'Brien uses the present tense when he comments on his own storytelling. Through this use of tense, he bridges his two discrete temporal settings: "Forty-three years old, and the war occurred half a lifetime ago, and yet the remembering makes it now."