Grass Valley is a small townsite 13 kilometres (8 mi) east of Northam, Western Australia in the Avon Valley area.
The town is named after a local property of the same name that was established in 1833 by William Nairn.
The Northam to Kalgoorlie Eastern Goldfields Railway line passes through the town and includes a crossing loop. The railway was built through the area in 1894. Land was set aside for a townsite in 1898 and the town was gazetted in the same year.
The surrounding areas produce wheat and other cereal crops. During its heyday of the 1950s–90s the town's local farmers were the largest producers of chaff (feed for racehorses) in Western Australia. The product was sought after by buyers throughout Western Australia as well as Asia and the Middle East. The town is a receival site for Cooperative Bulk Handling and had a Type B structure in the 1970s. The post office within the town is reputed to be the smallest in Australia. The town also has an excellent tavern dating back to the golden days of the once-important rail head.
The town is situated on the Golden Pipeline heritage trail. The pipeline passes through Grass Valley.