A filtered index might do the trick, but only for the condition defined to filter the index. With that, you simply query sys.dm_db_partition_stats, something like this:
SELECT SUM (row_count)
FROM sys.dm_db_partition_stats s
JOIN sys.indexes i ON i.object_id = s.object_id AND i.index_id = s.index_id
WHERE i.name = 'Index_Name';
Otherwise, the only option is to use a COUNT(*). A proper indexed table shouldn't have a problem with a query like that.
Luis C.
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