Presbyterians Today magazine reports that the 111th Congress of the US includes 44 Presbyterians -- 33 in the House and 11 in the Senate.
As I look at the list I see in the House there are 17 Democrat Presbyterians and 16 Republican Presbyterians; in the Senate there are 4 Democrats and 7 Republicans.
Therefore, a total of 21 Democrats and 23 Republicans in Congress.
Probably the two best known are Lamar Alexander (R-TN) and John D. Rockefeller (D-WV).