'hilly land' is correct and can be used in written English.
You can use it to refer to a geographical area with many hills. For example: "The hilly land in the Midwest is covered with lush green vegetation."
Cows grazed on the hilly land.
Only one-tenth of Arakan's generally hilly land is cultivated.
Malaysia is a hilly land with the gift of renewable energy resources.
The plateau, at an elevation between 660 and 1,970 feet (200 and 600 m), is composed of eroded hilly land surfaces, separated by steep, younger gorges.
The Chianina had been here as long as anyone could remember (da sempre, since forever), and you couldn't cultivate the hilly land without them.
Between Wittenberg and Dessau the east-west valley floor narrows to five miles in width, and hilly land rises to the north (the Fläming Heath) and south.
We studied 20 pedons in granitic hilly lands, loessial piedmont in granitic hilly lands, and piedmont plain in southern Mashhad, northeast Iran.
This study indicated that the cultivated hilly lands must be abandoned before a critical minimum SOM of 0·492%.
In Southeast Asia, upland rice (Oryza sativa) is an annual crop typically grown for subsistence on hilly lands that are at risk for soil erosion.
From 12,000 8300 cal BP, the sandy land landscape changed from desert to open elm forest and shrubland, while dry steppe dominated the hilly lands and patches of birch forest developed in the mountains.
Between 8300 and 6000 cal BP, elm forest was extensively distributed in the sandy lands, while typical steppe covered the hilly lands and mixed coniferous broadleaved forests expanded in the mountains.
