Extent and Shapefiles

[Camden Daily]

The units are determined by the projection type.  Different
projections have different units.

In your case, those are lat/long values in decimal degrees (dd).  The
values are both (x, y) pairs, so...

(-95.774704, 35.995683) - (-89.098843, 40.613640)

translates to

min_x = -95.774704
min_y = 35.995683
max_x = -89.098843
max_y = 40.613640

Curiously, could you tell me where you got the zip code shapefile? 
I've been trying to find a good one for the state of Illinois.

-Camden Daily
Prudential Preferred Properties
http://www.prupref.com