The Fences Between Us: The Diary of Piper Davis, Seattle, Washington, 1941 (Scholastic, 2010) by Kirby Larson is a very good book written in diary style. The story deals with a lot of issues of the war, but especially the incarceration of the Japanese.
Here's an intro to the story: Piper lives with her dad and sister in Seattle. Her brother Hank has enlisted in the Navy. Then the attack on Pearl Harbor happens. It's a while before they know he is okay and then the members of the Japanese Baptist church start getting arrested. Margie gets married and when Piper's dad decides to go to Eden, Idaho in fall of 1942 where his congregation has gone to Camp Minidoka, Piper has to go along. She ends up going to school in the camp and experiencing a lot of what the Japanese have to put up with except she gets to go home at night.
Kirby is the Newbery honor winner for Hattie Big Sky. Read about her other books on her website.