What is the history of the Mallory Wheeler Lock Company of New Haven,
CT?  Specifically, when were their locks marked with "M.W. & Co New
Haven"?  A complete answer would give the date of the founding of the
company and the date that company ceased operation (or continued under
another name).

I have found that Sargent & Co was the sole agent for M.W. from 1865
through 1878.  I need to know if the date range is longer than that.

According to Maud L Eastwood, in Antique Builders Hardware Knobs and
Accessories ppage 121 Mallory, Wheeler and Company was established in
1834 and went bankrupt in 1913

Thanks for the info.  That is a pretty long time span.  I was hoping
to pin-point the date for my door hardware more precisely. But this is
certainly a piece of the puzzle.

Maybe information about the house would be more useful:  when was it
built, was there a significant remodeling that could have led to new
hardware?

If the doorknobs are included, this is a serious collectors' field:

http://www.antiquedoorknobs.org/Feature.htm

And this could help too:

http://www.houseofantiquehardware.com/collector.htm

as well as other sites about antique doorknobs and hardware. 

Good luck, Myoarin