Allen is a city in Collin County in the U.S. state of Texas, and a northern suburb in the Dallas–Fort Worth metroplex. The population was 104,627 at the 2020 census, and was estimated to be 111,551 in 2022. Allen is located approximately twenty miles (32 km) north of downtown Dallas and is a part of the Dallas–Fort Worth metropolitan area.

The Allen area was previously home to the Caddo, Comanche, and other indigenous peoples. The first immigrants from the United States and Europe arrived in the early 1840s. The town was established by the Houston and Texas Central Railway and named in 1872 for Ebenezer Allen, a state politician and railroad promoter. The railroad allowed the sale of crops across the country before they rotted, causing a shift from the previous cattle-based agriculture. On February 22, 1878, a gang led by Sam Bass committed in Allen what is said to be Texas's first train robbery.

From 1908 through 1948, Allen was a stop along the Texas Traction Company's interurban line from Denison to Dallas. Allen was a small town of a few hundred residents when it was incorporated in 1953. Since this time, it has grown dramatically due to the construction of U.S. Route 75, the Dallas/Fort Worth International Airport, and the development of nearby Dallas and Plano. Among the more recent developments is the Shaddock Park neighborhood.

On May 6, 2023, a mass shooting occurred at the Allen Premium Outlets mall. Eight were killed, along with the shooter, and seven were injured.

According to the United States Census Bureau, the city has a total area of 26.48 square miles (68.58 km2), of which 26.40 square miles (68.38 km2) is land and 0.08 square miles (0.21 km2) is water.

Allen has a humid subtropical climate (Cfa in the Köppen climate classification), with long hot summers and cool winters.

In 2008, an EF-1 tornado touched down in Allen, damaging approximately 50 homes. In 2019, an EF-0 tornado touched down in west Allen.

As of the 2020 census, there were 104,627 people, 35,491 households, and 28,117 families residing in the city. There were 36,962 housing units.

As of the 2010 census, there were 84,246 people, 14,205 households, out of which 55.5% had children under the age of 18 living with them, 74.6% were married couples living together, 7.4% had a female householder with no husband present, and 15.2% were non-families. 11.9% of all households were made up of individuals, and 1.6% had someone living alone who was 65 years of age or older. The average household size was 3.07 and the average family size was 3.35. In 2019, 96% of adults living in Allen had at least high school degree and 55% had at least a bachelor's degree.

In the city, the population was spread out, with 34.9% under the age of 18, 5.4% from 18 to 24, 40.7% from 25 to 44, 16.2% from 45 to 64, and 2.8% who were 65 years of age or older. The median age was 31 years. For every 100 females, there were 99.7 males. For every 100 females age 18 and over, there were 97.3 males.

In 2019, 96% of adults living in Allen had at least a high school degree and 55% had at least a bachelor's degree. The average household income was $107,602. The city of Allen had 27,791 family units. The median age was 35.8 years. The median home value was $251,405. 59,620 of the population is currently registered to vote.

In 1992, Allen citizens approved the creation of the Allen Economic Development Corporation, which is funded by a 0.5% sales tax. According to the city government's 2014 facts & figures, the top employers in the city were:

According to the City's 2023 Annual Comprehensive Financial Report, the largest employers in the city are:

Allen serves as the corporate headquarters for the following companies: MonkeySports, CVE Technology, PFSweb, WatchGuard Video, PINSTACK, Boss Fight Entertainment, Brass Roots Technologies, Cytracom, No Magic, Lyrick Studios, WiQuest Communications, and Credit Union of Texas. Lyrick Studios ceased to exist in 2001 when it was purchased and incorporated into HiT Entertainment.

The city also has a 79,000-square-foot convention center (Watters Creek Convention Center) owned and operated by Marriott Hotels. In addition, Allen also has a multi-purpose arena, the 7,500-seat Credit Union of Texas Event Center, owned and operated by the City of Allen. There are three major malls/shopping complexes in the city: Allen Premium Outlets, Watters Creek, and The Village at Allen. These shopping complexes attract many visitors to Allen, Texas on a daily basis.

Allen has two major recreation centers: Joe Farmer Recreation Center and Don Rodenbaugh Natatorium. Don Rodenbaugh Natatorium boasts a large-scale indoor aquatic park with many swimming lanes, a rock-climbing wall, and a fitness center. Allen also boasts the Allen Community Ice Rink, Ford Pool, The Courses at Watters Creek, and Allen Senior Recreation Center. Most notably, Allen has The Edge Skate Park and Visitor Center, a 37,915-square-foot outdoor skate park making it one of the largest skate parks in Texas.

Allen is also home to 60 natural and man-made parks with over 1,188 acres of park land in total. Some of the more notable parks are the following: Allen Station Park, Bethany Lakes Park, Celebration Park, Glendover Park, Spirit Park, Stacy Ridge, Twin Creeks Park, Waterford Park, and Windridge Park.

Every year, Allen hosts the Allen USA Celebration on the last Saturday of June, which usually falls on the Saturday preceding the Independence Day holiday. The celebration boasts a large assortment of food trucks/stalls, sports drills, music concerts, a car show, bounce houses, and a large fireworks display - regarded as one of the largest in Texas. In previous years, there have been performances by Pentatonix, Jerry Jeff Walker, Vince Vance & the Valiants, Survivor, James "J.T." Taylor, Eddie Money, 38 Special, Three Dog Night, Commodores, Michael McDonald, and Lou Gramm. Now, the event draws in around 100,000 people annually and is considered to be the largest event in Allen.

In October 2004, the City of Allen purchased Chase Oaks Golf Club in Plano, Texas, adjacent to the southern city limits of the City of Allen. Chase Oaks, since renamed The Courses at Watters Creek, is a public golf course, and residents are entitled to discounted fees.

A multi-purpose arena, the 7,500-seat Credit Union of Texas Event Center, was completed in November 2009. It is home to the ECHL's Allen Americans, The North Texas Bulls of the National Arena League and the Dallas Sidekicks of the Major Arena Soccer League.

According to the city's most recent Comprehensive Annual Financial Report, the city's various funds had $160.9 million in revenues, $105.6 million in expenditures, $654.8 million in total assets, $125.6 million in total liabilities, and $42.5 million in cash and investments.

The city of Allen is a voluntary member of the North Central Texas Council of Governments association, the purpose of which is to coordinate individual and collective local governments and facilitate regional solutions, eliminate unnecessary duplication, and enable joint decisions.

The Allen City Council consists of the mayor and six council members, who are elected to serve three year terms. The council's responsibilities include planning and approving the budget, setting policy, enacting ordinances, establishing municipal law, regulating zoning, and appointing board and commission members. A professionally trained city manager manages day-to-day operations.

Appointments to City of Allen boards, commissions, and committees are typically two-year staggered terms, though some are three-year appointments.

Allen, like the rest of Collin County, was solidly Republican throughout the early 2000s, but through demographic changes it has shifted significantly towards the Democratic Party in recent elections, culminating in Democrat Joe Biden's narrow victory in the city in 2020.

The current state senator for Texas Senate, District 8 is Angela Paxton. Jeff Leach is the state representative for District 67 and Candy Noble is the state representative for District 89. Allen residents are represented in the United States Congress by Senators Ted Cruz and John Cornyn, and Representative Keith Self of Texas's 3rd congressional district.

Allen hosts a campus of Collin College, which is located inside Allen High School and mainly serves dual-credit high school students. A separate Collin College Technical Campus, opened in 2020, is located in west Allen. The 340,000 square-foot facility serves more than 7,000 students when fully occupied and is dedicated to workforce education.

The Allen Independent School District has 18 elementary schools, three middle schools, one freshman center (Lowery Freshman Center), an alternative education center, and a high school (Allen High School). Allen ISD serves almost all of Allen. Allen ISD opened a 111,000 square-foot STEAM center. It also serves as a location for elementary and middle school field trip experiences for enrichment on STEAM topics and experiences.

Small portions of the Allen city limits extend into Lovejoy, McKinney, and Plano ISDs. In the fall of 2006, new 9th grade high school students in the Lovejoy ISD boundaries began attending the newly opened Lovejoy High School. The school became a full 4-year high school in the 2009–10 school year.

Eagle Stadium opened on August 31, 2012, at a cost of $60 million and seats 18,000 people.

Allen High School offers advanced academic coursework through AP and IB courses. AP course enrollment is 53%.

The city of Allen possesses one sole library located in Downtown Allen: Allen Public Library. As of the 2019 City of Allen Facts and Figures, Allen has 147,772 volumes and 406,595 people were said to have visited the library.

Allen is served directly by several major roadways and freeways. Allen is bisected by U.S. Highway 75 and bordered to the west by Texas State Highway 121. Some of the major roadways in Allen are: Stacy Road, Exchange Parkway, McDermott Drive, Main Street, Alma Drive, Greenville Avenue, Ridgeview Drive, Allen Heights Drive, Angel Parkway, and Bethany Drive. Currently, with the large increase in its population and its ongoing retail and business development, traffic has become congested.

As of 2023, Allen is not served by any public transit agencies. The Dallas Area Rapid Transit (DART) public transit system does not extend north into Allen. Active Red Line service is unable to expand further north because Allen is currently unable to levy the 1% sales tax required for DART membership. Allen levies sales tax at the maximum rate of 8.25% set by Texas law. Redirecting 1% sales tax for DART membership would require scrapping funding for the Allen Economic Development Corporation and the Allen Community Development Corporation. The Texoma Area Paratransit System (TAPS) transit service provided bus routes for a short period from 2013 until Collin County bus service was suspended in 2015.