Sausthorpe is a small village and civil parish in the East Lindsey district of Lincolnshire, England, 8 miles (13 km) east of Horncastle and 3 miles (4.8 km) north-west of Spilsby. It lies on the southern edge of the Lincolnshire Wolds – a designated Area of Outstanding Natural Beauty – in the valley of the River Lymn. Farming remains the dominant economic activity in the area. The population was 305 in the 2011 census and estimated at 306 in 2019.

The River Lymn is a river in Lincolnshire, England. It rises in the Wolds on the eastern slope of Castcliffe Hill in Fulletby parish. It flows south-eastwards to the Lincolnshire Marsh, where it becomes known as the Steeping River on the boundary of Great Steeping parish. The main channel is supplemented by the Wainfleet Relief Channel as it passes Wainfleet All Saints, and the relief channel is joined by the old course of the Lymn. Once the two channels rejoin, there are three flood defence structures to protect the region from flooding by the North Sea.