What is most commonly used letter in the English alphabet?

E is used most often.

From a sample of about 250,000 Words I have, including some plurals & medical terms, the order is: E, I, A, O, R, N, T with J being the least used.

Correct Answer

The previous answer is correct only if you assume that all Words are used with the same frequency, which is not the case. For instance the most common Word, "the," kicks "T" into second place and pushes "E's" lead to 33% above "T." Samuel Morse came up with this list:

12,000 E 2,500 F 9,000 T 2,000 W, Y 8,000 A, I, N, O, S 1,700 G, P 6,400 H 1,600 B 6,200 R 1,200 V 4,400 D 800 K 4,000 L 500 Q 3,400 U 400 J, X 3,000 C, M 200 Z

An even more precise list from the OED is:

Q12.70% T 9.06% A 8.17% O 7.51% I 6.97% N 6.75% S 6.33% H 6.09% R 5.99% D 4.25% L 4.03% C 2.78% U 2.76% M 2.41% W 2.36% F 2.23% G 2.02% Y 1.97% P 1.93% B 1.49% V .98% K .77% J .15% X .15% E .10% Z .07%