Dead End in Norvelt by Jack Gantos 

Jack lives in a town named for Eleanor Roosevelt. It's summer, he's twelve and he's grounded for firing his father's Japanese sniper rifle, which was supposed to be unloaded.  Now, he's only allowed to help the elderly neighbor across the street, Miss Volker, who is the town medical examiner.  She also writes the obituaries of the original Norvelters as they die off.  She has severe arthritis in her hands, so she has Jack write and type-up the obituaries.  She also has him drive her to the houses of the deceased to examine the bodies.  She has put off another, annoying, Norvelter who has wanted her to marry him for decades, Mr. Spizz, an adult tricycle riding constable.  He sticks his nose into everyone's business and writes tickets because the grass is too high, or their house needs painting.  Jack's father comes home and orders Jack to do things that makes his mother mad.  In the meantime, Jack tries to figure out why so many of the old original Norvelters are suddenly dying.