For any real emergency, you would of course dial 911.  The numbers and locations below are for less critical problems.

The Lake Jackson community has a somewhat unique problem in relation to emergency services.  Because of the way the lots have been sold, combined and changed over the years, the street addresses of the homes are not always in order, or even directly related to the street the home is on.  Two houses that sit next to each other can have completely different street names in the addresses.  This problem is made even worse by the fact that many home's addresses are not visible from the street.  When emergency services are called to an address, they can  have difficulty  finding the correct house (this is also true for delivery services like propane, UPS, pizza, etc.)  There is actually a county code that requires that your house address must be visible from the street, primarily so that emergency services can find you.  You should make sure that the address posted is the same one that appears on your phone listing so that 911 calls are sent to the correct home.

Hospitals/Walk-in Emergency clinics 

Name	Phone	Address	Website	Directions
Prince William	(703) 369-8000	8700 Sudley Road Manassas, VA 20110	http://www.pwhs.org/pwhospital.shtml	Click
Altmed Urgent Care	(703) 361-4357	7320 Sudley Rd Manassas, VA 20109-2615		Click
Fair Oaks	703-391-3600	3600 Joseph Siewick Dr Fairfax VA 22033	http://www.inova.org/inovapublic.srt/ifoh/index.jsp	Click
Fairfax	703-698-1110	3300 Gallows Road  Falls Church, VA 22042-3300	http://www.inova.org/inovapublic.srt/ifh/index.jsp	Click

Law Enforcement

Name	Phone	Website
Non-Emergency Police/Fire	(703) 792-6500 (24 hour number)	http://www.co.prince-william.va.us/default.aspx?topic=040036000020000666  (provides numbers for specific departments)
Traffic Complaint Hotline	(703) 792-5919

Fire

Name	Phone	Address	Website
Lake Jackson Volunteer Fire & Rescue	(703) 368-3233	11310 Coles Drive, Manassas, Virginia 20112	http://www.ljvfd.com/

24 hour Veterinarians