Ever since settlers made the area their home prior to the American Revolution, Ohio's population has grown through immigration. Most early immigrants came from England, though large numbers of German and Irish natives also settled in Ohio. Prior to 1900, most foreign-born people living in Ohio came from Western Europe. By the second half of the nineteenth century, the source of immigrants became Eastern Europe. Polish, Hungarian and Czechoslovakian immigrants established communities in Ohio.
 
Ohio's population grew rapidly during the 1950s. Today, nearly 390,000 people living in Ohio were born outside the United States. About half of those people have become naturalized U.S. citizens. An increasing number of immigrants are being admitted to the United States each year with Ohio as their choice of intended residence. A large number (77 percent) of Ohio's foreign-born population age 25 and older has at least a high school diploma. Nearly 38 percent of the foreign born population over the age of 25 have earned a bachelor's degree.

Ohioans come from diverse ethnic backgrounds. The 2010 census counted more than 190,000 Ohioans of Asian descent. According to the U.S. Census Bureau, 6 percent of Ohioans speak a language at home other than English.

Immigration continues to be a source of new Ohio residents. One of the largest recent sources of immigrants is refugees from the African nation of Somalia. Since war broke out in Somalia in the early 1990s, Somali refugees have settled throughout the United States. The Columbus metropolitan area has one of the highest concentrations of Somali refugees in the entire nation. An estimated 45,000 Somali immigrants have settled in central Ohio in the past ten years.

One of Ohio's fastest-growing ethnic groups is the state's Spanish-speaking population. The 2010 census counted more than 350,000 Ohioans of Hispanic descent; a 40 percent increase from the 2000 Census. Most of Ohio's Spanish-speaking population is based in the state's larger cities.

One other community with large numbers in Ohio is the Amish. Ohio has one of the nation's largest populations of Amish, with an estimated 60,855 residents in 54 settlements (following only Pennsylvania). Ohio's largest concentration of Amish is in Holmes and Wayne Counties.