Mercer House (now the Mercer Williams House Museum) is an Italianate mansion at 429 Bull Street in Savannah, Georgia, United States. Completed in 1868, it occupies the southwestern civic block of Monterey Square in the city's Historic District.

The house was the scene of the 1981 killing of Danny Hansford by the home's owner Jim Williams, a story that is retold in the 1994 John Berendt book Midnight in the Garden of Good and Evil. The house is also featured in the movie adaptation of the book, released three years later. Williams held annual Christmas parties at Mercer House, on the eve of the Savannah Cotillion Club's debutante ball, which were the highlight of many people's social calendars. Williams had an "in" box and an "out" box for his invitations, depending on whether or not the person was in Williams's favor at the time.

After Williams's death in 1990, the house was owned by Dorothy Williams Kingery, Williams's sister. She died in 2023.

The home is open, in restricted form, to the public for tours. Kingery's daughter and Williams's niece, Dorothy Susan Kingery, manages the museum, which is based out of the carriage house at the rear of the property.