This will add the number of unique users to your query
WITH stats AS (
SELECT
LogonStats.DateTime,
LogonStats.IP
LogonStats.Logon
FROM LogonStats
WHERE DateTime >= DATEADD(day,-7, GETDATE())
)
,cnt AS (
SELECT Count(DISTINCT LogonStats.Logon) Unique_users
FROM stats
)
SELECT
People.FirstName,
People.MiddleName,
People.LastName,
People.Class,
Stats.DateTime,
Stats.IP,
Unique_users
FROM Stats
JOIN People ON LogonStats.Logon = People.ID
JOIN cnt
ORDER BY DateTime DESC