SF short story, maybe "House by the Side of the Road"? Human at remote interstellar site as first defense line against alien invasion, probably 1970s.
This isn't about a defense station in interstellar space. I am going primarily by the suggested publication date and the misremembered title, which sounded like something Simak might make up.
"Of course not," said Tyler. "Pluto never was a planet."
Instead, three astronauts are sent on a remote probe to Pluto and find an alien artifact.
The artifact is Pluto itself, a giant dust-covered hollow metal sphere. The explorers find a set of construction plans for the solar system.
But apparently things haven't turned out to plan.
Organic Marble mentioned Keith Laumer as a possibility. Laumer wrote a story that appeared in the April 1967 issue of Galaxy called 'Thunderhead'. Earth is at war with a spider-like race called the Djann. 20 years before the story opens, Lt. Carnaby had been dropped on an isolated Rim world to man a one-person sensor station. Unknown to him, the ship that set up the station was destroyed and the military authorities have forgotten it even exists. For years the Terran fleet has blockaded the Djann home system, but a Djann ship filled with eggs has pieced the blockade and is headed into the galaxy to set up shop somewhere else. Carnaby lures the ship to his planet with a phony Djann distress signal and then must face its crew alone...
"Let Me Live in a House" aka "A Friend to Man", a 1954 novelette by Chad Oliver; first published in Universe Science Fiction, March 1954, available at the Internet Archive; reprinted in Authentic Science Fiction, #70 June 1956, also available at the Internet Archive. You may have read it in one of these compilations.
The setting is a human outpost in space:
Four people, Gordon thought. Four people, utterly alone. Four human beings, pretending to be a society.
[. . . .]
It was all too plain that he couldn't contact Earth. His radio wouldn't reach that far, and, anyhow, who was there to listen at the other end? The ship from Earth wasn't due for another five months, so he could expect no help from that source. In an emergency, the two women wouldn't be of much help. As for Bart, what he would do would depend on what kind of an emergency he had to face.
There are four people (two married couples) at the outpost, not one; they are on Ganymede, not exactly "interstellar"; they are not there to guard against alien invasion, but they are visited by a space alien:
Gordon caught one thought and held on, desperately: If this is an alien, all that I have worked for is finished. The dream is ended.
The almost-man—changed. He solidified, became real. He was a man—elderly, a bit pompous, neatly dressed in an old-fashioned business suit with a conservative blue tie. He had white hair and a neat, precise moustache. His blue eyes twinkled.
"I am overwhelmed," he said clearly, waving a thin hand in the air. "My name is John. You are too kind to a poor old country boy."
Gordon stared. The man ws a dead ringer for the portrait of Grandfather Walters on the wall.
My identification is based mainly on your suggested title, which is part of a quotation from a poem by Sam Walter Foss which is featured in the story:
The two white cottages rested lightly on their fresh green lawns, like contented dreams. They were smug in their completeness. They had green shutters and substantial brass door knockers. They had clean, crisp curtains on the windows, and knickknacks on the mantelpieces over the fireplaces. They had a fragment of poetry, caught in dime-store frames in the halls: Let me live in a house by the side of the road and be a friend to man.
John faced Gordon, ignoring the other. His moustache bristled. He spread his hands helplessly. "I am a simple wayfaring stranger," he said. "I happened to pass by your door, and since you live in a house by the side of the road, I assumed that you wish to be a friend to man."
Gordon Collier started to laugh hysterically, but smothered it before the laughter exploded nakedly into the room. "Are you a man?" he asked.
"Certainly not," John said indignantly.
There was the bridge table, and there Helen and Mary and Bart, their cards in their hands, caught between action and non-action. There was the homey furniture, and the knickknacks on the mantelpiece over the non-functional fireplace. Out in the kitchen, the frigidaire wheezed. There was the line of poetry: Let me live in a house by the side of the road and be a friend to man. There was the portraid of old Grandfather Walters.
There’s a story by Gordon Dickson that also deals with the same subject, “The Steel Brother” (1952): it's about a lonely defender in a network of manned outposts in space that protect Earth from invading aliens who are prone to suicide by crashing against these outposts.
In his first battle, the protagonist is about to be overwhelmed as he decides to access some kind of neural link, where the ghosts of the previous defenders still survive. With their help he wins the battle.