There are many beaches along Oregon’s 363 mile coastline where you will find agates. On the North Oregon Coast, I would recommend beaches south of Cannon Beach such as Arcadia Beach or Short Sand Beach (Oswald West State Park). Further south, Oceanside is known for agates where at low tide you can pass through a tunnel at Maxwell Point to find gravel beds great for agate hunters.
On the Central Oregon Coast, the stretch of beach between Otter Rock and Newport are famous for agates, including the appropriately named Agate Beach. Further south you will find some good agate beaches between Yachats and Florence. Consider the beach access areas adjacent to small creeks such as Agate Point just south of Yachats, Neptune Beach or Stonefield Beach.
The quieter seasons of the year are often the best for agate hunters. Not only is there less competition for the prized stones, but off season storms often pull sand off the beach and waves dislodge agates from the shoreline revealing them to beachcombers. Look for areas of gravel deposits, then look closer to find the polished translucent quartz stones along with polished jasper and sometimes petrified wood and fossils.
Happy agate hunting!