The Ojibwe lived in the area for centuries before European contact, and were preceded by other cultures of ancient indigenous peoples.
The first European explorers were French, and they arrived in the area during the 17th century. Other early settlers were French fur trappers, who sometimes married Ojibwe women, and Jesuit missionaries. A Moravian colony was established in the county in the late 18th century. In addition to the original French and English settlers, later immigrants included Germans, Belgians, and others from Europe. In the 19th century the county received many American migrants from New York and New England, who were attracted to the area for land and booming jobs in the lumber and other resource industries.
Macomb County was formally organized on January 15, 1818 as the third county in the Michigan territory. The county was named in honor of Detroit-born Alexander Macomb, Jr., a highly decorated veteran of the War of 1812 and hero of the Battle of Plattsburg. He was made Commanding General of the U.S. Army in 1828. As was typical in development, it first encompassed a much larger area than at present. As population increased, the legislature removed territory in 1819 and 1820 to form the counties of Oakland, Lapeer, Genesee, and St. Clair.
In May 2008, Macomb County voters approved the inclusion of a County Executive in a new charter to be submitted to the voters by 2010. A charter commission was elected in November 2008 for the purpose of drafting a charter for submission to Governor Granholm, which was submitted and approved and placed on the November 2009 ballot. The Charter passed with a 60.4% to 39.6% margin.Mark Hackel was voted in as Macomb's first county executive.
According to the U.S. Census Bureau, the county has a total area of 571 square miles (1,480 km2), of which 479 square miles (1,240 km2) is land and 92 square miles (240 km2) (16%) is water. The county's southeastern border with Canada is located across Lake St. Clair.
Among Asian ethnic groups, six numbered over 1,000 people in Macomb County. The most numerous were the 5,713 Southeast Asian Indians, followed by Filipinos (4,155), Chinese (2,489), Koreans (1,853) Vietnamese (1,557), and Hmong (1,103). Pakistanis are also represented in Macomb County's population.
Native American tribes had over 2,478 residents in Macomb County in 2000.
In 2000, there were 309,203 households out of which 31.10% had children under the age of 18 living with them, 54.30% were married couples living together, 10.10% had a female householder with no husband present, and 31.80% were non-families. 26.90% of all households were made up of individuals and 10.30% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 3.09.
In 2000, the age distribution of the county was as follows: 24.10% under the age of 18, 8.00% from 18 to 24, 31.50% from 25 to 44, 22.80% from 45 to 64, and 13.70% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 96.00 males. For every 100 females age 18 and over, there were 92.90 males.
The median income for a household in the county was $52,102, and the median income for a family was $62,816. Males had a median income of $48,303 versus $30,215 for females. The per capita income for the county was $24,446. About 4.00% of families and 5.60% of the population were below the poverty line, including 7.00% of those under age 18 and 6.40% of those age 65 or over.
According to the 2006 American Community Survey the average family size was 3.15. The population of 25 and over was 571,463. 86.9% of that population had graduated from high school, and 21% of the population had a Bachelor's degree or higher. About 14.3% of that population was disabled. 12.5% of Macomb's population could speak another language at home.
The county government operates the jail, maintains rural roads, operates the major local courts, keeps files of deeds and mortgages, maintains vital records, administers public health regulations, and participates with the state in the provision of welfare and other social services. The county board of commissioners, which for the 2019-21 term is chaired by Bob Smith, controls the budget and creates and adopts ordinances and resolutions related to County functions. In Michigan, most local government functions — police and fire, building and zoning, tax assessment, street maintenance, etc. — are the responsibility of individual cities and townships.
In May 2008, Macomb County voters approved the inclusion of a County Executive in a new charter to be submitted to the voters by 2010. A charter commission was elected in November 2008 for the purpose of drafting a charter for submission to Governor Granholm, which was submitted and approved and placed on the November 2009 ballot. The Charter passed with a 60.4% to 39.6% margin.
The Macomb Intermediate School District serves all school districts based in the county.
Macomb County has shown Republican tendencies in statewide elections, while tending to favor Democratic candidates at the federal and local level. The county gained fame in the 1980s and '90s as a bellwether of state and national politics. Macomb's large cohort of working-class, socially conservative whites gave it one of the nation's most prominent concentrations of "Reagan Democrats". Outsider candidates with a conservative-populist bent have done well there in the past, such as Pat Buchanan in 1992 and Donald Trump in 2016. Macomb County voters were primarily responsible for the failure of the Regional Transit Authority proposal to create a public transit system in the Metropolitan Detroit region.
I-94 (Edsel Ford Freeway) runs –west through Detroit and serves Ann Arbor to the west (where it continues to Chicago) and Port Huron to the northeast. The stretch of the current I-94 freeway from Ypsilanti to Detroit was one of the first American limited-access freeways. Henry Ford built it to link his factories at Willow Run and Dearborn during World War II. It was called the Willow Run Expressway.
I-696 (Walter Reuther Freeway) runs east–west from the junction of I-96, I-275, and M-5 to I-94, providing a route through the northern suburbs of Detroit.
M-3 (Gratiot Avenue) is a major road that runs from Marysville to downtown Detroit. The portion of the road between 23 Mile Road and New Haven Road is not numbered. Between New Haven Road and Main Street in the city of Richmond the road is part of M-19. Between Richmond and Marysville the road is not numbered.
M-19 starts in New Haven goes up Gratiot to Richmond. The route leaves Gratiot and goes northwest through Richmond and then north through Memphis. Then it goes north through St. Clair and Sanilac Counties and ends at M-142 between Bad Axe and Harbor Beach in Huron County.
M-29 begins as part of 23 Mile Road, east of I-94 and ends in Marysville.
M-53 which is called the Christopher Columbus Freeway from 18 Mile Road in Sterling Heights to 27 1⁄2 Mile Road in Washington Township. It is also called the POW/MIA Memorial Freeway from 27 1⁄2 Mile Road in Washington Township to the freeway's end at 34 Mile Road in Bruce Township, however it is locally known as the Van Dyke Freeway. It continues as Van Dyke Road or Van Dyke Avenue north to Port Austin and south through Warren to Gratiot Avenue in Detroit.
M-59 (Veterans Memorial Freeway) from Utica to Pontiac, continues east as Hall Road to Gratiot Avenue and as William P. Rosso Highway to its terminus at I-94 and west as various surface roads to I-96 near Howell
M-97 (Groesbeck Highway) begins in Detroit at Gratiot (M-3) and ends at Hall Road (M-59).
M-102 (8 Mile Road), known by many due to the film 8 Mile, forms the dividing line between Detroit on the south and the suburbs of Macomb and Oakland counties on the north. It is also known as Baseline Road outside of Detroit, because it coincides with the baseline used in surveying Michigan; that baseline is also the boundary for a number of Michigan counties.
"Mile" roads: Surface street navigation in Metro Detroit is commonly anchored by "mile roads," major east-west surface streets that are spaced at one-mile intervals and increment as one travels north and away from the city center. Mile roads sometimes have two names, the numeric name (ex. 15 Mile Road) used in Macomb County and a local name (ex. Maple Road) used in Oakland County mostly.