Union County Oregon (Historic Districts) has 3 places on the National Register of Historic Places including 1 place of National significance and 1 place of Statewide significance. Significant places include Oregon Trail: La Grande to Hilgard Segment and Oregon Trail: La Grande to Hilgard Segment, La Grande Commercial Historic District, Union Main Street Historic District.
Some of the country's most noteable architects helped create the Union County places including Charles Miller and Calvin Thornton. Prominent architectural styles found in Union Country are Italianate, Early Commercial and Second Empire.