18 Republican presidents in the United States of America.
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There were 23 Democrats and 21 Republicans.
Rebublican presidents who served during the years 1900 to 1932 were McKinley, Teddy Roosevelt, Taft, Harding, Coolidge and Hoover. I count seven.
There have been 18 Republican presidents since the party was formed in 1854. The first was Lincoln who was elected in 1860 and the most recent was George W. Bush who left office in 2009.
10