Most of the characters (Seth Bullock, Al Swearengen, Sol Star, Reverend Smith, the Metz family, et cetera, in addition to the more famous Wild Bill Hickock, Calamity Jane, and Jack McCall), have real-life counterparts.
A feature film based on the series has been rumored for many years, but the cast has cited the difficulties of coordinating the schedules of everybody involved as a main obstacle. In 2016, HBO head Mike Lombardo said David Milch had pitched a general script, and that the network is fully committed to the movie.
Garret Dillahunt pursued the role of Seth Bullock, but Timothy Olyphant was already cast. The only role that was available at the time, was of Doc Cochran, so Dillahunt auditioned for that. He played the recurring role of Jack McCall in season one. Dillahunt was then considered for the role of George Hearst in season two, but it was decided that Hearst would not appear on-screen until the season finale. Dillahunt played the recurring role of Hearst's employee, Francis Wolcott.
Powers Boothe was originally cast as Al Swearengen. But Boothe fell ill before the pilot was to start filming. Boothe was replaced by Ian McShane, and then was given the supporting role of Cy Tolliver.
George Hearst was the father of William Randolph Hearst, the famous newspaperman on whom Citizen Kane (Citizen Kane (1941)) was based, and the great-grandfather of Patricia Hearst. When Hearst tells Merrick that he will start his own newspaper in Deadwood to tell lies for his side, it is a reference to the fact that W. R. Hearst is largely credited with the creation of the concept of "yellow journalism", and the use of his own newspapers to shape, and even create political and social opinion and actual events. The most famous example of this was what many historians characterize as W. R. Hearst's whole cloth creation of the Spanish-American War through his newspapers' inflammatory and lucrative headlines.
Until the end of season two, the character of Ellsworth did not have a first name. When it was decided to give him a first name, the actor portraying the role, Jim Beaver, requested that he be given the first name Whitney, after Whitney Ellsworth, Producer of Adventures of Superman (1952), whom Beaver knew from his research for a book on the life of "Superman" star George Reeves.
HBO offered the chance to David Milch to wrap the series in a shorter fourth season, but he declined to do it on those conditions. However, when Chris Albrecht was asked about it, he said that they also told Milch that HBO would give him a full twelve-episode season, if it was what he needed to wrap the show. Milch told them he would think about it over a weekend, but the news about the show possibly being cancelled reached the press to such a speed, that that conversation never happened, and Milch just moved on to develop John from Cincinnati (2007).
The role of Al Swearengen was originally written for Ed O'Neill. O'Neill screentested for the role, but HBO executives did not want to cast him, because of his fame as Al Bundy from Married with Children (1987).
According to a 2004 Jewish Journal of Greater Los Angeles interview with show creator David Milch, when John Hawkes first met Milch to audition for the role of Sol Star, Hawkes told Milch that he was not actually Jewish (unlike both the real-life Star and the "Deadwood" character). Milch's response was to ask Hawkes, "Have you ever felt shame or sadness or ostracized?" When Hawkes responded, "Every day". Milch told him, "Then you're Jewish."
Despite appearing in thirty-two out of thirty-six episodes, Jeffrey Jones (Merrick) was listed as a guest star in the first season. Similarly, Gerald McRaney (George Hurst) received a "special guest star" credit in season three, even though he appeared in all twelve episodes of that season.
The show's cancellation was a shock to the cast. During the third season, Timothy Olyphant and Ian McShane successfully renegotiated their contracts for higher pay, and HBO retroactively paid them the increased rate for the nine episodes of the season already shot. The show was cancelled a few weeks later.
Certain actors and actresses that were eventually cast in the series, initially auditioned for different roles. For example, Paula Malcomson (Trixie) initially auditioned to play Alma Garrett and W. Earl Brown (Dan Dority) pursued the role of Jack McCall.
Two actors in this series have daughters who played minor roles (as prostitutes). Parisse Boothe, the daughter of Powers Boothe, played Tess in five episodes, and Fiona Dourif, the daughter of Brad Dourif, appeared in three episodes as the "Chez Ami Whore".
Alice in Chains guitarist/vocalist, Jerry Cantrell, was a big fan of the show and appeared in the background in one scene in the first season. Cantrell is also good friends with actor W. Earl Brown, who made an appearance on the 2013 mockumentary Alice in Chains Twenty-Three.
The trivia items below may give away important plot points.
The series shows Seth Bullock and Sol Star witness Wild Bill Hickok's arrival in Deadwood. However, in reality, Wild Bill arrived in Deadwood two weeks prior to Bullock. Bullock arrived in Deadwood on August 1, 1876, the day before Bill was killed by Jack McCall.
The corset that Alma Garret (Molly Parker) takes off before sleeping with Seth Bullock (Timothy Olyphant) for the first time, is called the "Merry Widow". Appropriate, considering her husband's recent death.
In real-life, Al Swearengen was only thirty-one years old when Wild Bill Hickok was shot in Deadwood, At sixty-two, Ian McShane was older than the historical Swearengen's entire lifetime of fifty-nine years.