[4] In 1968, archaeologists from the Milwaukee Public Museum found human burials and artifacts, including stone altars, arrowheads, and pottery shards, during an excavation of one of the mounds.

[5][6] In the mid-1800s, Increase A. Lapham identified a group of circular mounds in the Saukville area and found a stone ax.

[7] An additional artifact of the early Native American presence in the Saukville area is the Ozaukee County Birdstone, discovered by a six-year-old farm boy in 1891.

[9] In the early 19th century, the Native Americans living in Ozaukee County included the Menominee, Potawatomi, and Sauk people.

The Menominee surrendered their claims to the land east of the Milwaukee River to the United States Federal Government in 1832 through the Treaty of Washington.

The Potawatomi surrendered their claims to the land west of the river in 1833 through the 1833 Treaty of Chicago, which (after being ratified in 1835) required them to leave the area by 1838.

The county was one of the areas affected by Wisconsin's "Great Indian Scare" of September 1862, in which some residents panicked because of unfounded rumors of a Native American uprising in the state.

[19] Several months after the panic, the United States Congress implemented the draft, which was unpopular among German immigrants with bad memories of mandatory conscription in their homelands.

From 1908 to 1940, the Milwaukee Electric Railway and Light Company (TMERL) provided electric interurban passenger and freight service from Sheboygan to Milwaukee with stops at Belgium, Port Washington, Grafton, Cedarburg, Thiensville, Mequon, and other villages as well as major road crossings within Ozaukee County.

The interurban cars ran approximately once per hour and delivered Ozaukee County agricultural products, such as milk and meat, to Milwaukee grocers and butchers.

[17] Ozaukee County's communities experienced significant population growth during the suburbanization that followed World War II.

[17] Communities that experienced the most significant population growth, such as Cedarburg and Grafton, began to annex agricultural land for residential subdivisions and retail commercial development.

The Wisconsin Shipwreck Coast National Marine Sanctuary was established in 2021 in the waters of Lake Michigan, with its southern portion lying off roughly the northern half of Ozaukee County′s coastline.

[29][30] Lion's Den Gorge Nature Preserve is a large bluffland and wetland county protected area on the shore of Lake Michigan.

The Association of Religion Data Archives reported that as of 2010, the largest religious group in Ozaukee County is the Roman Catholic Archdiocese of Milwaukee, with 28,644 adherents spread across eight parishes.

[39] Ozaukee County has a harbor in Port Washington on Lake Michigan, though not in the lakeside communities of Mequon or Grafton due to high bluffs along the lakeshore.

It runs through Grafton and connects to Sheboygan County and Brown Deer Trails via the old Milwaukee-Sheboygan Passenger Rail line.

Public transit was formerly provided by a commuter express bus (Route 143) to Milwaukee with stops in Port Washington, Saukville, Grafton, and Mequon.

The bus operated Monday through Fridays excluding holidays, and was run jointly by Milwaukee and Ozaukee County.

[44] Progressive judge Janet Protasiewicz received nearly 48% of the vote in Ozaukee in the 2023 Wisconsin Supreme Court election.