Try this:
SELECT t2.day, t1.HighestCount
FROM (
SELECT MAX(t1.count) AS HighestCount
FROM TableName
) AS t1 INNER JOIN TableName AS t2 ON t1.count = t2.count
or:
SELECT day, count
FROM (
SELECT day, count, ROW_NUMBER() OVER(ORDER BY count DESC) RowNo
FROM TableName
) AS t
WHERE t.RowNo = 1