Usually ‘farmstead by a spring or stream’, OE
wella +
tūn; examples include:
Welton East Riding of City & County of Yorkshire
Welleton (1086) (DB).
Welton le Marsh Lincolnshire
Waletune (1086) (DB). Affix means ‘in the marshland’.
Welton le Wold Lincolnshire
Welletune (1086) (DB). Affix means ‘on the wold(s)’ with loss of preposition, see
Wolds.