I want to know what country is Matt Groening from?

Matt was born in Portland Oregon. From what I've read, he feels that Comic Book guy is the most similar character to himself in the series.

Matt Groening is from America. He grew up in Portland, Oregon. Couldn't find who Homer was based on,(although that was Matt Groening's father's name) but here is something about Bart:

In an interview, Simpsons creator Matt Groening stated he chose the name as an anagram of brat. As all of the other Simpsons are named after and very loosely based off of members of Groening's own family, many naturally believe that Bart is specifically based off of The Simpsons creator himself. Groening has himself said in a DVD commentary that he had not so much in common with Bart when he was a child himself however, although he has never denied this claim either. Groening once said that Bart was partly inspired by the Diane Arbus photo "Child with Toy Hand Grenade in Central Park, New York City", but in the DVD commentary for Homer's Night Out he said that this relation between Bart and the child was false. He has also said that one of the inspirations for Bart was Groening's older brother Mark. Whether any of this is true or not is still unknown.

Groening has also stated that one of the biggest inspirations was the old Dennis the Menace TV series. The influence does not come from admiration, however. Groening has said that his desire to create came from the disappointing experience of watching the series premiere, which he described as "this namby pamby, Jay North type of show...". After this, he said he was inspired to create a character who was actually a menace.

The name Bart may also have come from the psychotic bad-seed child Bart who starred in V.C. Andrews’s incest romance novels which were wildly popular during the 1980s.

He's from America. Bart is just the letters from brat moved around. I pretty sure Homer has a little bit to do with Groening's dad.

He is an American cartoonist that was born in Portland, Oregon!

His father, a descendant of Russian Mennonites in Canada.

Beleive it or not... Groening named the main Simpson characters after members of his own family: his parents, Homer and Margaret!!! And his younger sisters, Lisa and Margaret :)

As for himself, he decided it was a bit too obvious to name a character after himself and chose the name "Bart" (an anagram of brat).

Groening says he refused to name Homer's dad after his father's real dad, leaving it to other writers to name that character. They gave him the name of Abraham, which by coincidence turned out to be the name of Groening's grandfather. Homer and Abraham are also the names of Groening's two sons.

Groening grew up in Portland, Oregon, and seems to have found names for some characters from major Portland street names such as Flanders, Lovejoy, Powell (as in Homer's half-brother Herb Powell), Quimby, Kearney (the bully), and Terwilliger (Sideshow Bob's last name).

Groening first conceived of the Simpsons in the lobby of James L. Brooks' office. He had been called in to pitch a series of animated shorts, and had intended to pitch his Life in Hell series. When he realized that animating Life in Hell would require him to rescind publication rights for his life's work, Groening decided to go in another direction. He hurriedly sketched out his version of a dysfunctional family. Reportedly, he designed the look of the Simpson family in only fifteen minutes!!!!

He's Canadian.

He has said that one of the inspirations for Bart was Groening's older brother Mark; but it's not known if this is true.

He's a proud Canadian!

AMERICA!!!!!!!!!!