Abstract: An apparatus for locking an enclosure cover, such as a manhole cover or enclosure lid, in seated engagement on its enclosure frame, includes a lock housing positioned within a lock aperture extending perpendicularly through the top surface of the enclosure cover. A reciprocating, manual throw bolt is inserted within an aperture extending laterally within the enclosure cover between the lock aperture and the side of the enclosure cover for releasable engagement into a receiving aperture within the enclosure frame. When inserted, the lock housing maintains the manual throw bolt in locking engagement with the enclosure frame. The lock housing includes a cylinder cam lock for releasably locking the lock housing in place within the lock aperture. The cylinder cam lock uses conventional keys that can be mastered or zoned. The locking apparatus can be retrofit into existing enclosure covers or included during initial manufacture of such covers.