Jeffco or JeffCo may refer to:
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Jefferson County, Colorado
Jefferson County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 582,910, making it the fourth-most populous county in Colorado. The county seat is Golden, and the most populous city is Lakewood.
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Jefferson County, Missouri transit (JeffCo Express)
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Jefferson College (disambiguation), multiple schools
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