Greg Koos is the Executive Director Emeritus of the McLean County Museum of History, a nationally accredited museum, in Bloomington, Illinois. He served in that museum from 1977 to 2016, 2019-20

His conference presentations and published writing includes histories of McLean County, studies on the material culture of American buildings, and studies of the Irish in the Midwest. He is currently researching Irish-born farmers in the Corn Belt 1840-1880. His book Freedom, Land and Community: A History of McLean County Illinois 1730-1900 was published in 2021. That work includes a contextual account of Irish immigration and community life 1853-1900. He is currently working on the Mississippi River as a channel of Irish immigration. In 2023 he was recognized by the Illinois State Historical Society by its Lifetime Achievement Award.