"Mingy" is a portmanteau word, a blend of "mean" and "stingy" which means, like its word sources, miserly, lacking in generosity, or just meager. It is pronounced with a soft G to rhyme with "stingy." It dates from the early 20th century, being first recorded in 1911. (Before that the word does seem to have existed in England and its colonies as a surname.)
MSN Encarta and a few British/American translation pages place the word geographically in the U.K. (and as an American I can testify I'd never heard it used here in the South, though Googling finds a few American uses mostly from the Northeast). It appears in British sources from D.H. Lawrence's 1928 Lady Chatterley's Lover to the 1967 song "Silas Stingy" written by the Who's John Entwistle. A.Word.A.Day's sample sentences were from Canadian and Australian sources, and a Google search turns it up in a Times of India restaurant review, so the word seems to have spread to other countries colonized by the British.
teleny offered: "Peg Bracken taught me this word. She defined it thus: a Highlander offered his daughter a shilling if she'd forgo dinner. She did, and put the shilling in a safe place while she slept. The Highlander took the shilling, and fined her breakfast for not taking care of her money."
The Irish Defence Forces seem to have a slang word of the same spelling but different source and nearly opposite meaning; one chaplain, Father Eoin Thynne, explains,
The Mingy Prayer Book, as it is known, derives its name from the Congo, where Irish military personnel served in the 60's. The traders who set up their stalls near the camp were often asked if they had a particular item in stock. Their standard reply was mingy, mingy, meaning many, or plenty. The word has taken on a richness of meanings far beyond its original commercial implications. Depending on the context in which it is used, it can convey approval or disfavour. The beauty of the word is that it means exactly what you want it to mean when you use it. Best of all, it's a word that is used and fully understood only by members of the Defence Forces and, to some extent, their families.