The Mary Valley is defined by the tourist railway between Monkland (Gympie) and Imbil, but its watershed is much more extensive. So, too, is the downstream section of the Mary River from Gympie to Maryborough.

The river was named in 1847 by the New South Wales Governor, Sir Charles Fitzroy, after his wife, Lady Mary Lennox. The Mary River was used for rafting timber during the early years of European land settlement, and the discovery of gold at Gympie in 1867 brought an inflow of miners and pastoralists. Alluvial flats along the Mary River and some of its tributaries were used for cropping, and there was small-time dairying in the 1880s.

The river's watershed, the 'greater Mary Valley', begins on the slopes of the Conondale Range, with the Yabba Creek and the Mary's own headwaters. From the western foothills of the Blackall Range there is the Obi Obi Creek which joins the Mary after collecting water from country with rainfall up to 2500 mm a year. The well-watered valley grows valuable hoop-pine forests, dairy pastures and has frequent floods.

After the federation drought dairying revived, and a butter factory opened in 1906. Dairying and closer-settlement farms were needed to offset the decline in mining in Gympie. The railway was proposed in 1906 and constructed in 1914-15 to Brooloo. The Mary Valley towns followed in quick succession, expanding from one-teacher schools to places with banks and schools of arts. Between 1915 and 1924 butter factories were opened at Gympie, Pomona, Cooroy and Maleny, all supplied with milk from farms along the Mary Valley or its headwater areas. The railway transported logs, livestock, vegetables, dairy produce and (later) students to Gympie High School. In the 1950s the Mary Valley was one of the most important dairying areas in Queensland, contributing 15% of the State's butter production (Queensland Agricultural Journal, December 1952). About half the area's butter came from the Gympie factory. Sown pastures supported 235,000 cattle and 35,000 pigs fed on skim milk.

The Mary Valley was lightly settled at its north and south ends before the railway, and school openings indicate the settlement pattern:

Place School
Lagoon Pocket
(a pasture area near Gympie)
1882-1970
Dagun 1924, current
Amamoor 1921, current
Kandanga 1915, current
Imbil 1897-1911
1915, current
(P-10, Mary Valley State College)
Brooloo 1907-70

The Mary River has carved gorges and ravines with its frequent onrushes of floodwaters, but above the river's edge much of the valley is undulating. Near Amamoor there is considered to be a high-potential water storage basin, Traveston Crossing, but it has its critics. Some say it is too shallow, and would inundate too much valuable farm land; and neither would it do much to hold back flood waters which have invaded Gympie about every ten years. In late 2009 the federal minister for the environment, under an international treaty for the protection of endangered species, refused permission for the dam and the project was abandoned by the state government.

During the 1970s-80s railway services were wound back. Pineapple growers kept them running in later years, but the goods service was replaced by the Valley Rattler tourist train in 1996. The valley is part of the Sunshine Coast hinterland, and beach-goers are invited to do a round-trip tour from Caloundra via the Blackall Ranges and the Mary Valley to Noosa Heads.

Further Reading: 

Murray Johnson and Kay Saunders, Wild heart, bountiful land: an historical overview of the Mary River Valley, Runcorn, Queensland State Archives, 2007

A. Hegarty,'Agriculture in the Mary Valley and adjoining districts', Queensland Agricultural Journal, December 1952, p 311