North Carolina from the NC GOP site
I am cutting and pasting what I see as pertinent information. Each individual county can have additional rules.
http://www.ncgop.org/getactive/join.asp
A. MEMBERS
All citizens of North Carolina who are registered Republicans are Members of the Republican Party of North Carolina and shall have the right to participate in the official affairs of the Republican Party in accordance with these rules. All reference herein to Delegates, Alternates, Officers and Members shall, in all cases, mean persons identified and registered with the Republican Party in the Precinct of their residence. Any person running for an office within the North Carolina state, district legislative, county or precinct Republican Party shall be a resident of the jurisdiction in which he seeks office.
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3. Election of Delegates (EDIT: at precinct level)
The annual Precinct Meetings shall elect 1 Delegate and 1 Alternate to the County Convention. They shall also elect 1 additional Delegate and Alternate for each 100 registered Republican voters, or major fraction thereof, in the precinct as of January 1 of that year. In determining the number of registered Republicans to be used as the basis for the number of additional Delegates and Alternates to be elected in the precinct under this calculation, a County may adopt, in its Plan of Organization, a basis number of registered Republican voters less than 100 but, in so doing, must assure proportional representation of all registered Republican voters in the county.
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iii. The County Convention shall elect 1 Delegate and 1 Alternate to Congressional District and State Conventions, plus 1 additional Delegate and Alternate for every 250 Republicans, or major fraction thereof, registered in that county, as of January 1 of that year. Each County shall further elect 1 Delegate and Alternate for each Republican elected to the state legislature and to public office on the state or national level from said County in the last election held for that office. With respect to the District Convention, the additional 1 delegate and 1 alternate shall only be elected to the District Convention being held in the District in which said Republican elected to the state legislature and to public office on the state or national level actually lives.
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ARTICLE V - CONGRESSIONAL DISTRICT ORGANIZATIONS
A. CONVENTIONS
1. Call of Convention
a. A Congressional District Convention shall be called in every year by the Chairman of the Congressional District Committee, within the month of April upon 20 days written notice of the time and place for holding same to all Members of the District Committee and to the County Chairmen within said District.
b. At the time of the call of the Convention, the District Chairman shall appoint a Credentials Committee, which will meet and issue its report on Delegates and Alternates certified to that Convention at least 3 days in advance of the convening of the Convention. All Delegates and Alternates challenged in the report of the Credentials Committee shall be notified prior to the day of the Convention and allowed to present their case to the Credentials Committee prior to the convening of the Convention. The Delegates and Alternates elected in the County Conventions, unless successfully challenged, shall sit as Delegates and Alternates to the Congressional District Convention.
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2. Convention Action
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d. In every Presidential Election Year the Congressional District Convention shall elect 3 Delegates and 3 Alternates to the Republican National Convention and shall nominate 1 Presidential Elector, who must not be a current elected public official (pursuant to state law).
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I hope that is helpful.