Mattachine Midwest (/ˈmætəʃiːn/ MA-tə-sheen) was a gay rights organization active in Chicago, Illinois, United States. It was established in 1965 during the homophile movement and for several years operated as Chicago's major gay rights group. However, it lost this status during the gay liberation movement in the early 1970s and shifted its aims away from political activism and towards offering social services. At its peak in 1979, it had 150 members. However, in 1986, the group dissolved due to a declining membership and lack of leadership.

The organization stemmed from earlier efforts in the 1950s and early 1960s to sustain a local presence of the national Mattachine Society in Chicago. However, the failure of these efforts led local activists to believe that the formation of an independent organization was necessary. Additionally, activists believed that a local organization could help to address the recent uptick in police harassment, as the police in the early 1960s had been conducting an increased number of police raids on gay venues. In particular, several historians point to the 1964 Fun Lounge police raid as the main impetus for the formation of this new organization.

The organization was officially established in 1965, with activists Bob Basker, Pearl M. Hart, and Valerie Taylor among the founding members and William B. Kelley and Marie J. Kuda joining early on. In addition to monthly meetings, the organization published a newsletter and hosted a helpline that members of the community could call for things such as legal aid or religious assistance. Regarding legal aid, the organization had several attorneys that helped represent gay men in legal affairs and engaged in political activism against police harassment. Following the 1969 Stonewall riots and the emergence of the gay liberation movement, the organization lost its standing as Chicago's premier gay rights organization and began to shift away from political activism and towards social services. This included, among other things, the creation of discussion groups for gay alcoholics and for parents and friends of gay men. However, by the mid-1980s, the group was experiencing a dwindling membership and a lack of direction regarding the role it played in the gay community, and in 1986, it was dissolved.

Multiple historians cite the organization as one of the first successful gay rights groups in Chicago, and in 2002, it was inducted into the Chicago LGBT Hall of Fame. Additionally, in 2005, Chicago History published its first article on the LGBTQ history of Chicago, with the focus being on the history of Mattachine Midwest. Historians have also noted the importance of the newsletter in documenting the gay history of Chicago, with journalist Tracy Baim calling it a "treasure trove" of information on the topic. Much of the organization's records are housed in the Gerber/Hart Library and Archives.

Among the earliest records of LGBTQ history in Illinois come from the 1920s works of German American immigrant Henry Gerber. In 1924, he created the Society for Human Rights, which was the first gay rights group established in the United States, and published a periodical entitled Friendship and Freedom. However, in 1925, the Chicago Police Department conducted a police raid Gerber's house and arrested him and others associated with the organization. While charges against Gerber were eventually dropped, the raid brought about an end to the society, and it would be about 30 years before another gay rights group was established in Chicago.

In 1950, the Mattachine Society was established in Los Angeles as an advocacy group for gay men. Around the same time, the Daughters of Bilitis was established to serve a similar role for lesbians. These groups were part of the homophile movement of the 1950s and 1960s, which sought to integrate LGBTQ individuals into mainstream society by winning support from experts in the medical and psychological fields instead of through direct political activism. Over the next several years, local chapters were established across the country, and by 1955, both groups had a Chicago chapter. However, both of these organizations, based on the West Coast of the United States, struggled to maintain their presence in Chicago. The Mattachine chapter had been established in 1954, and by the following year, the national organization reported that there were three groups in the area operating under the Chicago Area Council of the Mattachine Society. However, this presence became defunct within the next several years. In 1959, it was revived by activist Pearl M. Hart, though this new group, called either Chicago Mattachine or Mattachine of Chicago, collapsed within a few years.

While the Mattachine presences in Chicago had engaged in some political activism during its existence, they functioned largely as a social group for LGBTQ people. However, by the mid-1960s, several LGBTQ activists in Chicago were pushing for increased activism in response to an increase in harassment from police. In 1961, the government of Illinois had repealed their sodomy laws, becoming the first state in the United States to decriminalize homosexual acts between consenting partners. However, according to historian John D'Emilio, "almost as a response, police stepped up their tactics against 'public' sexual activity". This included, among other things, more frequent raids on gay bars. For instance, in April 1964, the Fun Lounge police raid resulted in the arrests of about 100 people who had their names, addresses, and places of employment published in local newspapers, such as the Chicago Tribune. Multiple sources, including Chicago LGBTQ historians Tracy Baim and Marie J. Kuda, cite this raid in particular as the main impetus for the formation of a more politically active gay rights organization.

In early 1965, LGBTQ activists Bob Basker, Hart, and Ira Jones met to discuss forming a new Mattachine organization in Chicago. At the time, there were only two LGBTQ organizations in Chicago: a Daughters of Bilitis chapter and a conservative chapter of One, Inc. Later that year, Mattachine Midwest was established by the following people: Basker, Hart, Jones, Bruce C. Scott, and Valerie Taylor. The name had been recommended by gay activist Craig Rodwell, while Chuck Renslow, a local proprietor of gay establishments, secretly financed the organization. According to the Encyclopedia of Chicago, this new organization was led by Basker and Hart, with the former serving as the founding president. In addition to the founders, William B. Kelley and Kuda were among the organizations first members. Membership was largely kept secret so as to protect individuals who had not yet come out, and early on, many members used pseudonyms. Unlike previous Mattachine organizations in Chicago, this new organization was an independent entity not directly affiliated with any other Mattachine Society. The formation of this new group was part of a larger trend in the 1960s that saw the formation of several gay rights organizations in cities across the United States that included, among others, the Janus Society in Philadelphia, the Personal Rights in Defense and Education in Los Angeles, and the Society for Individual Rights in San Francisco.