When the book opens, the four March sisters, Meg, Jo, Amy, and Beth, live in rural New England during the Civil War. The name of the town is Plumfield, but the setting is likely Concord, Massachusetts, the historic town in which Louisa May Alcott, the author, lived when she was growing up. The March girls' father is working as a chaplain in the war, and the year is likely 1862 or 1863 (when the war's outcome is still in doubt). The book opens at Christmas, when the girls mourn the loss of their family's wealth, but they wind up giving their presents to the poor.

Later, Amy visits Europe with her wealthy aunt, and Laurie, their neighbor, also goes to Europe with his grandfather. Jo leaves New England to live for a while as a nanny in New York City, where she also tries to be a writer. At the end of the book, Jo returns to her family's house in New England. 

When the novel begins, it is Christmastime. We know the novel is set sometime during the early 1860s because Mr. March, the girls' father, is away serving as a chaplain for the North in the Civil War. When the book opens, it is likely 1861 or 1862 because it doesn't seem as though the war has been going on for very long at this point. Early in the story, while the March sisters are complaining about all the things they don't have, Jo says,

"We haven’t got Father, and shall not have him for a long time." She didn’t say "perhaps never," but each [of her sisters] silently added it, thinking of Father far away, where the fighting was.

Later, Mr. March actually sustains an injury during his service and is sent home.

As far as geographical setting, the novel takes place in New England, though the town in which the March and Lawrence families live is never explicitly named. Most readers agree the location seems to be based on Alcott's home in Concord, Massachusetts, but this is never directly stated in the story.