Cucumber Salad Mold

1 (3 oz.) pkg. lime Jello
1/2 c. diced celery
1 1/2 c. water
2 tsp. grated onion
2 T. lemon juice
1 c. mayonnaise
1 c. minced seeded cucumber
1/2 c. sour cream

Dissolve Jello in 3/4 cup boiling water. Add remaining 3/4 cup water and lemon juice. Chill until partially set. Add remaining ingredients and beat together. Pour into 5-cup mold and chill until firm.