Militia Lists
Hertfordshire has a very comprehensive set of Militia lists from the period 1757 to 1801. These record the names of the men in the parish who were liable to serve in the County militia, and is in effect a census of most of the adult males between the ages of 18 and 45.
The list did not include those who had already served, and peers, clergymen, teachers, magistrates, apprentices, soldiers, seamen and constables were not eligible. Those who were infirm, or had a large number of dependents could be granted exemptions. The lists sometimes contain occupation, family and infirmity information.
Further information on the Hertfordshire holdings of militia lists at HALS is given in the book Tracing Your Family History in Hertfordshire. The Hertfordshire Family History Society has produced excellent booklets which index the lists of each parish, and which can be purchased from their web site.
Militia lists have proved useful in the following answers:
CHARGE, Little Hadham, circa 1800
GURNEY, Wigginton, 18th century
CATO, Kimpton (& Tring), 19th Century
If you can add to the information given above tell me.