SourceIp from LoginHistory object/entity can be used to query Salesforce users using specific Login IP.

SourceIp from LoginHistory object/entity can be used to query Salesforce users using specific Login IP.

Sample SOQL:

SELECT Name
FROM User
WHERE Id IN (
SELECT UserId
FROM LoginHistory
WHERE SourceIp = 'x.x.x.x'
)

Replace x.x.x.x with the IP Address to check.