Whether your last name is MacEachern, McEachern, McEachren, McEachran or any other variety of ways to spell the name, we're all from the same clan.   You are welcome here.
What is in a name?   The question has been asked many times.   Our Gaelic name is MacEachtighearna, which when translated means "Son of the Horse Lord".   Mac or Mc?   Doesn't really matter, they both have the same meaning; "Son of".   Although I use the Mac in my spelling, I have documents showing both being used for my father, grandfather and great grandfather.   EACH in Gaelic means "horse".   TIGHEARNA means "Lord", as in
Suipeir an Tighearna (The Lord's Supper) and not Morair which is an English title.   Before 1000 A.D. there were no sir names used in Scotland as we know them but each individual had a single name.
The MacDonalds and the MacEacherns were closely associated as clan's that occupied territory in the same district of Scotland- mainly Kintyre and the Western Isles.   The McDonald's were a large clan and as Lord of the Isles they were a powerful clan and had the use of swords, horses and soldiers of other clans in the district, including the MacEacherns, MacAllisters and MacInnis.   But this circumstance alone did not make these clans septs of the McDonalds.   On a manuscript written during the reign of Charles II, there is mention of a MacEachern in the Council of the Lords of the Isles in Mull.   The last Clan Chief of the MacEacherns was John MacEachern.
Britain Express (web site) has a great wealth of information about the MacEachern Cross in Campbelltown.