Union lies in the extreme southeast corner of the Grande Ronde Valley near the western edge of the Wallowa Mountains.
Oregon Route 237 runs through the city between Cove to the north and North Powder to the south.
Oregon Route 203 also passes through Union, linking it to La Grande, about 20 miles (32 km) to the northwest.
Catherine Creek, a tributary of the Grande Ronde River, passes through the city.

According to the United States Census Bureau, the city has a total area of 2.50 square miles (6.47 km²), all of it land.
Union lies in the extreme southeast corner of the Grande Ronde Valley near the western edge of the Wallowa Mountains. Oregon Route 237 runs through the city between Cove to the north and North Powder to the south. Oregon Route 203 also passes through Union, linking it to La Grande, about 20 miles (32 km) to the northwest. Catherine Creek, a tributary of the Grande Ronde River, passes through the city.
According to the United States Census Bureau, the city has a total area of 2.50 square miles (6.47 km²), all of it land.
Union, Oregon