If you try the ispell command get the following:
Starting new Ispell process ispell with en dictionary...
apply: Searching for program: No such file or directory, ispell
Install ispell with brew
$ brew install ispell
Things should just work.
If you get an error like the following you might have a configuration that is pointing you to a different hash
Starting new Ispell process ispell with en dictionary...
ispell-init-process: Can’t open /usr/local/Cellar/ispell/3.4.00/lib/ispell/en.hash
For example here I had an eval-after-load that set the directionary to en. The change to american is shown below.
ls -al /usr/local/Cellar/ispell/3.4.00/lib/ispell
lrwxr-xr-x 1 brad admin 16 Feb 9 2015 american.hash -> americanmed.hash
-r--r--r-- 1 brad admin 1386144 Feb 9 2015 americanmed.hash
-r--r--r-- 1 brad admin 24095 Feb 9 2015 english.aff
lrwxr-xr-x 1 brad admin 16 Feb 9 2015 english.hash -> americanmed.hash
(eval-after-load "ispell"
(progn
(setq ispell-dictionary "american"
ispell-silently-savep t)))