West Allis has been portrayed as a decaying manufacturing town for years, but in 1900 a site west of the city was chosen for a huge new manufacturing facility. The construction of this huge facility began at the site that served as the terminus of a spur railway connecting the two railway lines. The construction of such a facility would act as a catalyst for the development of suburbs in and around Westallis and ensure adequate rail transport for other industries.

The state fair in North Greenfield stimulated progress in housing, industry and commerce. The facility allowed public transportation to and from Milwaukee to be brought to the area.

West Allis is represented in the United States House of Representatives by Tammy Baldwin (D-Milwaukee), a member of the Wisconsin Republican Party. In the Wisconsin State Assembly, West Allis was joined by Sen. Joe Chisholm (R-Waukesha) and the state Republicans Leah Vukmir and Mark Pocan, both Democrats, represent West All in the Wisconsin state Senate. Since its inception, BlueLine has served as a public-private partnership between the City of Milwaukee and the Milwaukee County Board of Supervisors. Former Milwaukee City Council member and Green Bay County Executive Tom Barrett, who was elected in spring 2018, has since moved to the city.

After serving in the Civil War, he developed an interest in horse racing, where he gained a reputation as a breeder and trainer of trotting horses. Wadhams "Oriental Station was incredibly successful, leading to a significant expansion of the company's operations in West Allis in the late 19th century. In 1901, the company became AllIS Chalmers, and a large new production plant was built next to the existing plant. Other industrial companies, including General Electric, Coca-Cola and General Motors, and others, also established factories in and around West Allis.

The fair has been held in West Allis since its inception in 1876, and some of the historic highlights of the fair include the visit of President Hayes in 1878, when Abraham Lincoln was running for president, the visit of President Franklin D. Roosevelt in 1865 and the election of George W. Bush in 1888.

The West Allis Library was the product of a steel magnate who financed the construction of the city's first public library on the corner of North Main Street and North Avenue in 1876. The library, designed by architect Edwin O. Künzli, served the western Allied community until 1989, when a new facility was opened. The prefabricated building was rebuilt in front of the present building, which was built around 1887. It was then used as a library for the school district and later as an elementary and middle school by the West Alli School Board.

The Allis - Chalmers Corporation built a clubhouse at the corner of North Main Street and North Avenue in the early 20th century to allow the company's employees and their families to participate in social and recreational activities on the company's premises.

On the fairground near the Pettit National Ice Center, they defeated the University of Wisconsin-Madison 27-0 in the first round of the World Junior Hockey League playoffs.

West Allis, which emerged from the Depression of the 1930s, experienced a new phase of growth immediately after World War II, and remained a vibrant manufacturing community until the early 1970s. In the 1990 "s, it weathered several long recessions, the worst of which occurred in the early 1980" s, characterizing a strong economic recovery and the creation of a number of new businesses, such as Wal-Mart.

The site became the permanent home of the Wisconsin State Fair, but it wasn't until 1892 that the fair was held at its current location, on the site of a former train station on the west side of the city.

Between 1902 and 1906, West Allis High School, the first public high school in Wisconsin, became part of the village school system. On April 2, 1906, Governor J.O. Davidson declared West Allis "the first and only Wisconsin village with its own school district" and on April 3, 1908, the first city council.

Much of the housing growth has taken place in what is now South 56th Street. The population was distributed across the city, with 17.2% 65 years or older and the median income per family was $50,732. According to the U.S. Census Bureau, the median household income in this city was $39,394 in 2010, up from $37,834 in 2007.

In the 1950s, the city government annexed much of the South 56th Street area of West Milwaukee. A production company bought a 100-acre lot at the corner of South 57th Avenue and South 52nd Street. The Allis Company sold the 100-acre property on the south side of East 55th Street to the City of Milwaukee and the Wisconsin Department of Natural Resources for $25,000.

Before the 1880s, the site of the new facility was called Honey Creek and was temporarily called North Greenfield. After the incorporation of the village on 31 May 1902 (census 1018), the name West Allis was adopted. At that time it was North Greenfield, and at some point it was called North Greenfields.