Mumby is a village in the East Lindsey district of Lincolnshire, 33 miles E of Lincoln and 2½ miles from the North Sea coast at Chapel St Leonard's. The church is on the main road through the village and is built of limestone ashlar, squared limestone and greenstone rubble. It consists of a 13thc. nave with clerestoreys and four-bay side aisles. The three W bays of the N arcade have transitional piers and responds of Romanesque style. The W tower is in a Perpendicular style. The church was restored in 1843-4; the long chancel being rebuilt in 1874.

Earnwig had 3 carucates of land here in 1966, and in 1086 it was held by Eudo from Count Alan of Brittany. Gilbert de Ghent also held 2 berewicks, or outlying estates, here, of 2 and 4 bovates, and Eudo Spirewic held 6 bovates in demesne.

Originally the side aisles of the nave were of three bays, these being bays 2-4 today. A 13thc. extension of the nave resulted in the addition of the eastern-most bay as demonstrated by the rectangular pier with responds E and W, the lower height of the capitals in bay 1, the different label profile of bay, and the chamfer treatment of the arris on the rectangular pier, this later feature belonging also to the chancel arch and bay 1 of the S arcade. The S arcade has moved thoroughly into the Gothic.

The label stops must surely be 13thc despite the Romanesque appearance of the dragons. They, as much as the W respond capital, point to the survival of Romanesque motifs into the 13thc.