1931 was a year in the 20th century.
In relation to 1885
- Eastern Auto Sales
- El Kid
- Essex Theater
- Hill Valley High School
- Hill Valley Police Department
- Majestic Arms Inn
- O'Malley & Sons Barber Shop
- Hill Valley Stationers
- Hill Valley speakeasy
- Lamont's House of Ermine
- Law Offices of Gale, Zemeckis, & Fine
- Bank (1931)
- Sisters of Mercy Soup Kitchen
- Town Theater
- Hal's Hardware
- An arson attack occurs on the Hill Valley speakeasy.
- Emmett Brown, who is found unconscious at the scene, is believed to be the suspect and is arrested under the pseudonym "Carl Sagan."
- The automatic retrieval system of the DeLorean is eventually activated which sends the time machine to May 14, 1986.
- June 13, Saturday: Marty McFly arrives to rescue Doc in the past.
- Date Unknown, August: Frankenstein plays at the Town Theater.
- Tuesday, August 25: Trixie Trotter turns on Irving "Kid" Tannen after being mistakenly informed that he has murdered Arthur McFly. Tannen is subsequently arrested by Officer Danny Parker, who is promoted to detective shortly thereafter.
- Mid—Late 1931: The Hill Valley mayoral elections are held.
- Monday, October 12 to Thursday, October 15: The Hill Valley Science Expo is held.
- Tuesday, October 13: Edna Strickland is arrested for arson after her return from 1876.
- Saturday, June 20: James Tolkan (who played James Strickland and Gerald Strickland) is born in Calumet, Michigan.
- Saturday, September 12: Bill McKinney (train engineer of Locomotive 131) is born in Chattanooga, Tennessee.