According to the Encyclopaedia Britannica, which you can probably find at your local library and which you may have electronic access too, mosquitoes are " any of approximately 3,500 species of familiar insects in the fly order, Diptera" and the "duration of the life cycle varies greatly depending on the species." The Britannica discusses three major types of mosquitoes, whose life cycles range from ten days to several months.

Grzimek's Animal Life Encyclopedia, which, again, you may have either hard copy or electronic access to at your local library, contains an eighteen page article on the order Diptera, but it does not list any specific life cycles for mosquitoes prevalent in north America.

A search for mosquito life cycle in Google brings up a number of potentially helpful documents. You may be able to find what you are looking for there, or to narrow down the search by selecting a type of mosquito you are interested (for instance, those that carry West Nile virus or those that carry malaria). Any general encyclopedia at your library will also possibly have helpful information, and if you are near a large public or university library, there may be specialized entomology encyclopedias that could help you.

Sources
Diptera (Mosquitoes, Midges, and Flies). Natalia von Ellenrieder, PhD. Grzimek's Animal Life Encyclopedia. Eds. Michael Hutchins, Dennis A. Thoney, and Melissa C. McDade. Vol. 3: Insects. 2nd ed. Detroit: Gale, 2004. p357-374. 17 vols.

"mosquito." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 10 Aug. 2007 http://search.eb.com/eb/article-9053915. (note: this link will only work if you have a subscription to the Britannica)