An Arkansas contractor taking work in Missouri deals with the same four questions everywhere: who licenses the trade, when a licence is actually required, when workers compensation kicks in, and where the business registers. Below is Missouri's answer to each, with the agency's own link.
Licensing
No statewide general contractor licensing; local rules apply. Missouri Division of Professional Registration handles state-licensed occupations
No statewide general contractor license; cities and counties license contractors and most construction trades locally. The Division of Professional Registration offers a voluntary statewide electrical contractor license.
Workers compensation
Missouri Department of Labor and Industrial Relations, Division of Workers' Compensation
Required with five or more employees; construction-industry employers must carry coverage with one or more employees.
Business registration
Missouri Secretary of State, Corporations Division
New hire reporting
Most states require newly hired employees to be reported within a short window of their start date.
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Starting or running the business itself is covered in the contractor business guide. Arkansas licence records for Benton and Washington counties are in the contractor directory.