Check your contractors license certification based on the state they are registered in:

Alabama

Alabama Licensing Board for General Contractors

http://genconbd.alabama.gov/

Alaska

Regulations of Construction Contractors

https://www.commerce.alaska.gov/web/cbpl/ProfessionalLicensing/ConstructionContractors.aspx

 Arizona

Arizona Registrar of Contractors

https://roc.az.gov/

Arkansas 

Arkansas Contractors Licensing Board

http://www.aclb.arkansas.gov/

California 

Contractors State Licensing Board

http://www.cslb.ca.gov/ 

Colorado 

Denver Contractor License Search

https://www.denvergov.org/contractorlicenses 

Boulder Colorado Licensed Contractor Search

https://bouldercolorado.gov/plan-develop/hiring-a-contractor

Connecticut 

Connecticut eLicense Verification System

https://www.elicense.ct.gov/

Delaware

State of Delaware License Search

Florida

My Florida License Search

https://www.myfloridalicense.com/wl11.asp

Georgia 

Georgia Professional License Search

http://verify.sos.ga.gov/Verification/

Hawaii

Hawaii Professional & Vocational Licensing Search

https://pvl.ehawaii.gov/pvlsearch/

Idaho

Idaho Building Safety Permit and License Lookup

https://web.dbs.idaho.gov/etrakit3/ 

Illinois 

Illinois Contractor License Search

http://publicrecords.onlinesearches.com/Illinois-Contractor-Licenses.htm

OR

Illinois Department of Financial & Professional Regulation

http://www.idfpr.com/licenselookup/licenselookup.asp

Indiana 

Indiana Online Licensing Search

https://mylicense.in.gov/EVerification/Search.aspx

Iowa

Iowa Contractor License Search

http://www2.iwd.state.ia.us/contractor.nsf

Kansas 

Licensed Contractor Search Johnson County

http://www.jocogov.org/dept/planning-and-codes/cls/search-licensed-contractor

OR

Licensed Contractor Search Kansas City

http://www.kcmo.org/Codes/faces/selectcl.jspx?_afrWindowMode=0&_afrLoop=452123016964091&_adf.ctrl-state=qa7i7geyh_4

Kentucky 

Bowling Green Licensing Board

http://www.bgky.org/

OR

Louisville Licensing Board Permit and Licensing Search

Louisiana 

Online Contractor Search

http://www.lslbc.louisiana.gov/contractor-search/

Maine

Maine Professional & Financial Regulation Board

http://www.maine.gov/pfr/index.shtml

Maryland 

Maryland Licensing Queries

https://www.dllr.state.md.us/pq/

Massachusetts

Massachusetts License Lookup

http://elicense.chs.state.ma.us/Verification/Search.aspx

 Michigan

Residential Builder and Maintenance & Alteration Contractor Company License

http://www.michigan.gov/statelicensesearch/0,4671,7-180-24786-81518–,00.html

Minnesota

MN Department of Labor & Industry

https://secure.doli.state.mn.us/lookup/Licensing.aspx

Mississippi

Mississippi State Board of Constructors

http://www.msboc.us/?page_id=122

 Missouri

Missouri Division of Professional Registration

https://renew.pr.mo.gov/licensee-search.asp

Montana

Montana Department of Labor and Industry

http://erd.dli.mt.gov/work-comp-regulations/montana-contractor/icec-search

Nebraska

Nebraska Contractor Search

https://dol.nebraska.gov/conreg/SearchContractors/SearchContractors

Nevada 

Nevada State Contractors Board

https://www.nvcontractorsboard.com/datamart/nvscbSearchByBusiness.do?from=searchType

New Hampshire

State of New Hampshire License Verification

https://nhlicenses.nh.gov/MyLicense%20Verification/Search.aspx

New Jersey 

New Jersey License Search

New Mexico 

New Mexico License and Regulation Department

https://public.psiexams.com/index_login.jsp

New York 

Home Improvement Contractor License Verification

http://www1.nyc.gov/nyc-resources/service/2952/home-improvement-contractor-license-verification

North Carolina

North Carolina Licensing Board For General Contractors

http://www.nclbgc.org/lic_fr.html

 North Dakota

Contractors Licensed in North Dakota

http://sos.nd.gov/business/contractors/contractors-licensed-north-dakota

Ohio 

Ohio Department of Commerce

http://www.com.ohio.gov/dico/ocilb/

Oklahoma

Oklahoma Construction Industries Board

http://cib.ok.gov/

 Oregon

Oregon Construction Contractors Board

http://search.ccb.state.or.us/search/

 Pennsylvania

Home Improvement Consumer Information

http://hicsearch.attorneygeneral.gov/

Rhode Island 

Rhode Island Registration/License Status Lookup

http://www.crb.ri.gov/search.php

South Carolina 

South Carolina Department of Labor, Licensing and Regulation

https://verify.llronline.com/LicLookup/Contractors/Contractor.aspx?div=69&AspxAutoDetectCookieSupport=1

South Dakota 

South Dakota Department of Labor and Regulation Licensee Roster

https://sdrec.sd.gov/registration/licenseelist.aspx

Tennessee 

TN Department of Commerce and Insurance License Search

http://verify.tn.gov/

Texas 

Texas Department of Licensing and Regulation License Data Search

https://www.tdlr.texas.gov/LicenseSearch/

Utah

Utah Licensee Lookup and Verification

https://secure.utah.gov/llv/search/index.html

Vermont

The State of Vermont does not license general contractors or home improvement contractors.

Virginia 

Virginia License Lookup

http://www.dpor.virginia.gov/licenselookup/

Washington 

Washington State Department of Labor and Industries

https://secure.lni.wa.gov/verify/

West Virginia

West Virginia Department of Labor (Contractor Licensing Board)

Wisconsin 

Wisconsin Department of Safety and Professional Services

http://dsps.wi.gov/Licenses-Permits/Credentialing/Trades-Professions

Wyoming

Cheyenne Contractor Licensing Board (MUST CALL)

http://www.cheyennecity.org/index.aspx?NID=314

Natrona County Contractor List (MUST DOWNLOAD LIST)

http://www.natrona.net/index.aspx?NID=436

Casper Contractor Licensing (MUST CALL)

http://www.casperwy.gov/residents/property_and_housing/building_and_inspections/contractor_licensing