I am missing relatives that are nowhere and am now wondering if, when they did the census from 1851 on did they do census in the Mental Asylums, if so where are they located. I am looking mainly for the Middlesex Ontario area

Mental asylums were enumerated but not under the same schedule as the personal census. Schedule A was the personal census, Schedule B was the agricultural census. Institutions were enumerated under a different schedule - to find this schedule consult the microfilm itself as only Schedules A and B were made available online at Library & Archives Canada. Note that these schedules were only microfilmed for the 1851, 1861 and 1871 census returns.