Their original territory was in present-day Missouri and Kansas but they were gradually pushed west by European-American pressure and treaties.

Osage has an inventory of sounds very similar to that of Dakota, also a Siouan language, plus vowel length, preaspirated obstruents and an interdental fricative (like "th" in English "then").

In contrast to Dakota, phonemically aspirated obstruents appear phonetically as affricates, and the high back vowel *u has been fronted to [y].

[2] Osage is among the few indigenous languages in the United States that has developed its own writing system.

The Osage Language Program, created in 2003, provides audio and video learning materials on its website.

[3] The 2nd Annual Dhegiha Gathering in 2012 brought Osage, Kaw, Quapaw, Ponca and Omaha speakers together to share best practices in language revitalization.

It most commonly conflates with /i/ following ð and n. Usually in fast speech, unstressed /a/ is pronounced [ə].

Listed below is some features and phonological alternations of Osage: The dentalveolar obstruents are often fricated: the ejective always (though it has other sources as well), and the other series before the front vowels /i ĩ e u/.

(The fricated allophone is written c.) Č, hč are rare, and only found in diminutives: č only in two words, čóopa 'a little', čáahpa 'squat', and hč for hc in endearment forms of kin terms like wihčóšpa 'my grandchild'.

Consonant clusters of the type CC only occur in initial and medial positions.

[7] The initial clusters are [pʃ] [kʃ] [tsʼ] [st] [sts] [sk] [ʃt] [ʃk] [br], excluding aspirated stops.

The former derives from historic *xl, the latter from *kð and *gð; these sequences have largely merged with simple *l. This is productive; ð in verbs may become l when prefixed with k. The r is apparently an approximant like English [ɹ].