I heard somebody ask this question and was then curious about it too. Whay does the U.S have a mid-west when some of the states in the mid-west are really more mid-east? Why isn't Kansas and other states located almost dead center referred to as middle U.S??? Is there a reason or is it just the way it is? Thanks!

While I don't know when the term "Midwest" came into use, I do know that at its inception, the US had no land west of the Mississippi. Thus, Ohio really was in the midwest of the country. The Northwest Territory, the first possession of the United States, was located just west and south of the great lakes, and east of the Mississippi. Ohio, the easternmost part of the Territory, was part of the NW Territory, and as was Illinois, Wisconsin, and Minnesota, the westernmost part of the territory. Michigan and Indiana, were included in the Territory.
Another point to remember is that, for most of its history, the population center of the US was east of the Mississippi. (While Chicago is a strange place for a university called Northwestern Univeristy, the name really did make sense at one point.)
Another consideration is the dates of statehood for most of the truly western states. Look at the dates below.

State/Entry granted
36. Nevada Oct. 31, 1864

37. Nebraska March 1, 1867

38. Colorado Aug. 1, 1876

39. North Dakota Nov. 2, 1889

40. South Dakota Nov. 2, 1889

41. Montana Nov. 8, 1889

42. Washington Nov. 11, 1889

43. Idaho July 3, 1890

44. Wyoming July 10, 1890

45. Utah Jan. 4, 1896

46. Oklahoma Nov. 16, 1907

47. New Mexico Jan. 6, 1912

48. Arizona Feb. 14, 1912

49. Alaska Jan. 3, 1959

50. Hawaii Aug. 21, 1959

Thanks Dorian!!

"While I don't know when the term "Midwest" came into use..."

Etymology online gives 1889 for midwestern and 1929 for midwest (of course, this is the first recorded use their sources found, which is not necessarily when the term was first used).