Why would pin 1 be true

When run pin_1_State shows true or a value of 1
with no input
Can not figure why

int pin_1_State = 0;
int pin_2_State = 0;
int pin_3_State = 0;
int pin_4_State = 0;
int pin_5_State = 0;
int pin_6_State = 0;
int pin_7_State = 0;
int pin_8_State = 0;
int pin_9_State = 0;
int pin_10_State = 0;
int pin_11_State = 0;
int pin_12_State = 0;
int pin_13_State = 0;
int sensorValue = 0;
float voltage = 0;

void setup()
{
//start serial connection
Serial.begin(9600);
//configure pin1 - pin12 as a digital input
pinMode(1, INPUT);
pinMode(2, INPUT);
pinMode(3, INPUT);
pinMode(4, INPUT);
pinMode(5, INPUT);
pinMode(6, INPUT);
pinMode(7, INPUT);
pinMode(8, INPUT);
pinMode(9, INPUT);
pinMode(10, INPUT);
pinMode(11, INPUT);
pinMode(12, INPUT);
pinMode(13, OUTPUT);
}

void loop()
{
pin_1_State = digitalRead(1);
pin_2_State = digitalRead(2);
pin_3_State = digitalRead(3);
pin_4_State = digitalRead(4);
pin_5_State = digitalRead(5);
pin_6_State = digitalRead(6);
pin_7_State = digitalRead(7);
pin_8_State = digitalRead(8);
pin_9_State = digitalRead(9);
pin_10_State = digitalRead(10);
pin_11_State = digitalRead(11);
pin_12_State = digitalRead(12);
sensorValue = analogRead(A0);

voltage = sensorValue * (5.0 / 1023.0); //0-5v
Serial.println(pin_1_State);
Serial.println(voltage);

}

Because pin 1 is used by the serial. You can't use serial AND pin 1 (nor pin 0) at the same time.

pin_7_State = digitalRead(7);
pin_8_State = digitalRead(8); // smiley <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
pin_9_State = digitalRead(9);

Good reason for using code tags…

pin_7_State = digitalRead(7);
  pin_8_State = digitalRead(8);  //no smiley <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
  pin_9_State = digitalRead(9);

Doh I never knew that
So basically do not use pin 1 or 2

basically do not use pin 1 or 2

0 or 1, actually. They can be used if you're NOT using the serial port. But pin0 will always act like it has a pullup resistor, since it will still be tied to the USB/Serial chip (through a resistor.)

Even if your not using serial functions in your sketch, wiring external components to pins 0 and 1 can make it so you can not upload new sketches to your board unless you remove the components from those two pins.