CREATE TABLE table_39621 ("School" TEXT, "Mascot" TEXT, "Location" TEXT, "Enrollment" FLOAT, "IHSAA Class" TEXT, "IHSAA Football Class" TEXT, "# / County" TEXT)

What's the enrollment at 41 Johnson?
SELECT AVG("Enrollment") FROM table_39621 WHERE "# / County" = '41 johnson'
SELECT AVG("Enrollment") FROM "table_39621" WHERE "# / County" = '41 johnson'