Welton Le Marsh is a village and civil parish in the East Lindsey district of Lincolnshire, England. It is situated approximately 6 miles (10 km) north-east from the town of Spilsby and approximately 5 miles (8.0 km) south from the town of Alford. The hamlet of Boothby lies within the parish about 1 mile (1.6 km) east of Welton Le Marsh village.
The parish church is dedicated to Saint Martin and was medieval, but rebuilt in 1792 of stone and brick, and restored in 1891. It is a Grade II* listed building.
A Neolithic flint axe and perforated stone hammer head were found here in 1948 and 1906. A Bronze Age flanged axe was found just outside moated area at Hanby Hall Farm.
The remains of a motte are located about 275 yards (251 m) east of Hanby Hall Farm. The motte is about 5.5 yards (5.0 m) high, and surrounded by a ditch.
Thwaite Hall is a Grade II listed building, reputedly part of a former Augustinian Priory, with attached cottage; the present house dates from the 14th century. The Lincs to the Past website describes it as the site of an Augustinian Cell belonging to Thornton Abbey which was recorded in 1440 and which still existed in 1536.
Welton Le Marsh has a local public house, The Wheel Inn.
Also within the parish is Candlesby Hill Quarry, a nature reserve which was once Gunby estate chalk pit. It is Site of Special Scientific Interest (SSSI) maintained by the Lincolnshire Wildlife Trust.